Txwelder

Truck in sig, Predator on tow tune. Ranch hand front and rear bumpers so weight added there. 35's and 2" leveling kit. Staying between 70-75 mph, only got 15 mpg on the highway. Hooked up the fifth wheel, checks in about 7500 lbs, dropped to 8 mpg. Is this comparable to other trucks with similar mods?

92'1stGen

Is that hand clac'd or based on the overhead? If it's hand calc'd, that's fairly respectable with those specs. I get 17 - 18 hwy in my 06' 3500, stock w/ 4.10's.

Txwelder

I always hand calculate and my mileage/speed is based on my GPS, not my odometer/speedometer.

cdennyb

It doesn't say in your sig whether or not you changed the rear end ratios when you went to the BIG tires, if not, then you're getting mileage based on those big tires and poor ratio choice. Just a thought.
Better fuel mileage is a function of many variables, many of which you indicate you've violated, (e.g. 70+ mph, big tires, trailer, etc.) so if you ran with the cruise control at a decent speed of say 60 mph and had the rear end ratios changed to compensate for the tire size, you might see much better numbers, like 15-17 on the highway and close to 12-14 pulling.
Keep in mind, the use of more slippery lubes in everything will help a lot too. Rear end lube, trans fluid, engine oil, wheel bearing grease to name a few.
The easier your truck rolls the better fuel mileage you'll get.
I'd say you're getting the mileage that's reflective of the mods you have. Not saying that's bad, just saying that's what you;ll get with it set up like you have it.

Shorts

Do you know your rpm at that speed? Just curious as I was thinking there's room for improvement. For 70-75mph unloaded, yes 15 is good. Can't say for towing that setup.

Danavilla

Iff you're towing at anything approaching those speeds, you shouldn't expect any better. You're pushing huge amounts of air with the fiver. My mileage drops 1/2 mpg or more with every 5 mph over 55

truckbouy2

One word....Yup.

Lost Lake

My BFG's were 305's at 34" and they gave me good mileage.
My Dura's were 34" and gave me good mileage.
Now I run 35" Nitto Trails and a leveling kit and the mileage fell hard.

I am getting 15 in the winter and around 16-17 in the summer. I was easily getting 19 during the summer and could eek it out to 24 if I babied it on stock tires.

15 on the highway is still bad. I can still get 18 highway if that's all I do, but in town and on hills just kills my mileage. Rolling at 62 steady, 18 is no problem. That's taking into account my overhead is 18% optimistic. The overhead has to read 22 for my hand calcs to be at 18.

Rednax

I sold my gasser because that was the mileage I was seeing. Current numbers in sig.

Slow down to 65. No truck handles well enough, solo or towing, to travel at 70 or above. Let the idiots flow around you, pack by pack, and enjoy a more relaxed ride that is cheaper mile-by-mile . . you'll arrive at the same time anyway. No lane changes, no braking, just easy on-the-cruise-control.

Check the basics:

CAC leaks
alignment
tire pressure
filters
brake drag

(and do them on the 5'er, too).

.

C Schomer

I test drove a used 04.5 auto 3.73 and tall tires before I found my 03. The tall tires absolutely ruined that truck! The truck was a slug, the gears were way far apart and it always felt like the engine was laboring. Have you tried the econ/100hp tune? I run that one 99% of the time. Tow tune is just noticeable. Extreme is a blast and I can get every bit as good of mpg with it as with econ but it's hard to do with the atomic throttle response. I have the puck but I RARELY stack cuz the pred. adds plenty by itself. Craig

rjjr

Wind speed and direction will make a HUGE difference especially when towing a load.

Dodgezilla

Mileage will go up dramatically if you slow down to 65 or less. In my truck it seems like I lose 1 mpg for every 2-3 mph I go over that. At 80 mph my numbers are the same as my in-town mileage. 60mph is where I have gotten my best of about 23mpg. Very hard to drive that slow though and kind of dangerous too. You know you're driving slow when you are even ticking off the Prius owners when they have to get around you....

Txwelder

I drove an entire tank never exceeding 55 mph, all highway. Still only squeezed out high 15's. My gears are stock. I disagree with your assessment when talking about highway driving. The taller tires should compliment the mileage at highway speeds. In town, yes, 35's and 3.73's are going to drink fuel. Im going to put the 100 hp tune on and slow down to see what happenes.

jerry007

I drove 505 miles on 27 gals. of fuel. All of the miles were no load, driving at 65 mph. When I keep the rpm's at 2,000 or less I get better mileage. Truck is all stock. I have 4:10 gears and its a 2 wheel drive.

VADERPOWER

tex, if u drove on an entire tank never exceding 55 and got only high 15s, there something wrong with your truck, period. i had 315bfgs on my truck and at 55 i was easily over 20 hand calced. any chance u could have a dragging brake? does your truck coast easily when u put it in nuetral? my truck with 4.10s and 285s going only 55 on the highway, can get 22+ quite easily. do u run max pressure in your tires? this makes a HUGE difference imo.
just rotate them often,every 4000miles.