Rednax

Nice to see FE shown as an average. All other numbers are B.S. since they're so easily manipulated.

A good driver gets 30% better mileage than the bad driver, at a minimum. The good driver has skills the bad driver doesn't.

I run the miles at 1700-1900, town or country. No exceptions. My average mpg in signature. The only time I drop below 20 mpg around town is in summer due to extended idling for A/C.

You can read the stickies at ECOMODDER. There are a few diesel truck owners over there. Current high is 30+ mpg average in a CTD (on his work commute). 1,100-miles per tank.

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Grit Dog

You're not doing that bad. Seems a bit low, as my (wifes) Mega 4wd on 285's pulls avg 17.5-18mpg summer, about 1mpg less winter. Mixed unloaded driving, 30% in town, 70% 75-80mph on the freeway.
3.73's with a G56 and 33" tires.
Maybe it's the bumper knocking you down a tad?
My truck seems to do a little better with the camper shell (flush w/ top of cab) on it than the tonneau cover.
What do you have for 34" tires? I'd like to go taller but not wider. 285-75s or 255-85's?
BTW I could never go 70mph across rural Montana!
The 60mph speed zones here in Seattle (jsut moved) are killing me!

And yes I think most of the 20mpg or more claims are bs or driving 55mph.
I can get my fuel econ display to get up to 20-21mpg if I got the cruise set at 55. It's pretty accurate now with the bigger tires and uncorrected speedo compared to hand calc taking into account the tire diameter.

dslpwr81

I have 275/65/20 Hankooks. Believe there 34.07" tall and around 10" wide. Also, I corrected my speedo with the Smarty. Seems to be accurate. I've done the whole 3600 seconds in 1 miles etc... math equation probably a hundred times to see if my speed is accurate, and its always right on. I'm just not achieveing what others are I guess. I'll play around with the Smarty on different setting to see about gaining a little. I do crazy overkill maintainence on my truck too, so I know theres nothing holding my mileage back there. I'm to the mind set now, that some trucks just simply achieve better mileage than others, even when there identical.

Spooler

WOW, seams like you need to work the crap out of that thing. These trucks don't do very well being babied all the time. Work that thing!!!!!

062500

I have a stock 06 with 3.73 rears. I have put 55000 miles on it and I am very carefull so as to maximize my mileage. I get 11.5 to almost 13 around town and the most I have gotten on a trip is 15.9.

MDCS

Hi Jason! I was looking over your numbers and the only difference between your mileage and mine is the in town numbers. My truck gets a very repeatable 17.4 mpg combined average. That is to say that my standard drive to work is 11.5 miles, 7 stops, average speed is 40 mph. This makes up about 70% of the driving. the other 30% being urban routes and freeway.
I can't speak for the effect the mods on your truck are having, but as mine is stock and the numbers are close, I would say the answer is none. The key to mileage with these Gen III trucks is RPM. As our effective final drive ratios are close ( yours is 2.84, mine is 2.94 without the O/D unit), I will say that you are turning about 2400 rpm at 70. Like driving a Singer Sewing machine, ain't it? You have to find a way to get your rpm down. With my Gear Vendors the truck turns 1850 at 70 and gets 21 mpg on the highway (actual speed was closer to 75 and there was some city mixed in before I filled up). Bigger tires may help but there is a definite point of diminishing return. If you aren't in the mood to spend $3500 on an O/D unit, there is the option of 3.42 gears. This would get you about a 20% drop in rpm at any given speed. I am guessing this change would cost you about $850 an axle (someone more knowledgeable than I can chime in on the price). After the price, the only down side is the effect the taller gear would have on towing. Having the auto tranny might help out here.
The big fix is really the cam! This EGR in your mouth crap is just killing these motors! Add to that the soot trap (Cadillac converter) and these things might as well have a bunch of bananas in the tail pipe (There is a rant that goes with this, something about burning 25% more fuel to save what, but that is for a different thread)!
Any way you slice it, it is gonna cost you money to save fuel. The last option is to sell your ' 06 and buy say, a '96? Good luck.

JT

jon05ctd

Speed kills....... mileage.
I just got back from a 1600 mile road trip. The best I achieved was 18.98 mpg (Hand calculated)This was 60-65 plus Washington DC. site seeing.
'The worst was coming home running anywhere from 0-80 traffic, highway, and construction which was 17.49 mpg.

shep1

I seem to get my best when I keep the RPM's at 1625. I'm not a speeder though. About 41mph without TC and 60mph with TC. gives me 17-18.5 around town mixed highway and side streets.
lower 20's on long highway trips

Grand Geek

No one brought up tire weight... It DOES make a big difference.. Check out the actual weight of your tires then compair to other tires the same size.. I keep going back to goodyear MTR's in a 305/70 17.. It seems your 06 and my 04 are set up darn near the same. 4/10's auto i have a leveling kit in the front and a topper level with the cab. Front buck stop bumper and i put the warn 16.5 ti in it. I get close to 800 miles per tank when i keep the speeds at 65 mph on the highway..

Rednax

This is my highway rpm. 58-mph. Never falls below 24-mpg, loaded or empty while solo. Around town I look for 1,700-1,900 rpm and either adjust speed or choose another gear.

sturgeon

First check the air and fuel filters. Every single truck has a "sweet spot" in cruz mode. it's when the engine operates at it's most eficient given the current conditions. The best way(and most exspensive way is to use a digital fuel flow gauge...see mythbusters) to find what mph works best for your truck, it's normaly a perticular rpm range and not mph, we found this by going from the factory tires to 19" tires, it was the same rpm that produced the best fuel flow. Again, every single truck is it's own algorithym with the two biggest variables being the air and fuel filters.

GLHS

I am spending nearly $12,000 in fuel running my 03, 2500, 6 speed, 4x4, 3.73, 285/70/17s and am interested in improvements.

I have only a Smarty Jr and an ATS intake horn as mods.

I average approx 15 mpg with my setup; Cm flatbed with 4 under bed toolboxes and a #2000 two wheeled trailer. I think I am around 11,000-12,500GVW most of the time.

Which of these do you guys think might help the most?

Synthetic oils in differentials. $120
Turbo from an 04.5+ engine. $350-$550
Aftermarket exhaust manifold. $350-$650
Free spin kit. $1700
PSM cold air intake and smooth hose kit. $280
Changing gear sets to 3.42. $1200
Front end alignment. $60

Any other ideas?

I have noticed the biggest improvement so far is not flooring it to get it moving from a stop.

Big Horn 06

My truck is weird. Case in point, it's my daily driver and with Smarty Sr on 5, gets 16-17 around town with a best of 22 on the highway going 70 mph. I hooked up an open car trailer with a '65 Cutlass, turned down Smarty to 1 and drove from Los Angeles to Reno via US 395. I was at 60 mph since the speed limit for trailers and trucks here is 55. LA to Bishop, no a/c, topped off, averaged 16.9. Bishop to Reno, bunch of high altitude climbing and maintaining said 60 mph without breaking a sweat, topped off in Reno, 14.4, Reno to LA non stop with a/c on, 16.3. I get the same mileage towing 3 tons as I do doing the daily driving thing.

BLACKBEAR

Air your tires to the max then see what mileage you get. If it don't help then drop it to where you had it.

Rednax

Pictures always help. A flatbed isn't aero (the highway mpg problem) but there might some ideas to help that. Other than that, synthetic fluids, new filters, elimination of steering slop and brake drag and CAC leaks plus a perfect alignment are on the table. Not "okay" but perfect. The best mechanical baseline pays more than just returning truck to stock mpg levels.

The next step is records. "Approximately" and "I think I am" are not acceptable. Log every gallon. Put the rig on a three pad certified weight scale (CAT Scale) and get the numbers set up. 1,2,3 mpg changes are meaningless . . what you want to know is the percentage increase
as the only thing that counts is the average annual mpg.

Spending money to save money is backwards, ain't it? While it is possible that some changes may be beneficial, you'd be better off in understanding, first, how the money actually works. For that it is records and understanding CPM costs. Cents-Per-Mile, not just of fuel, but of all costs. Fuel cost can change via driver/owner input, but fixed costs are higher and have more meaning. IOW, decreasing cpm a little may not mean as much to you by comparison. And spending a bunch of money on the truck may actually take you backwards. HIgher mpg, but increased fixed cost.

Start with some pics, tell us how you're using it, and get the separate scale numbers for both vehicles (plus combined). We need to see the truck FA and RA, both hitched and unhitched. Set up a logbook (or spreadsheet). Start your own thread, if you want. But don't go spending any money just yet (past re-establishing mechanical baseline).

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