Drove from Phoenix to LA with the cruise set at 70 mph. No wind,just cruising along. The over head read 19.2 or so and then when I got into stop and go/slow freeway driving it went up to 20.2 and then drove out to Sagus with some hills and when I stoped for gas the over head was reading 19.5 and hand figured to exactly 18.5. Had the dealer set it for the bigger tires and the odo/speedo is dead nuts on.So this sure ain't what everyone else claims to be getting. I am turning 2200 rpm at 70mph and thats with 34 inch tires pumped up to near max.All filters are good too. The best mileage I have ever seen is in slow freeway traveling.
I know the stick is hurting me and the width and print of the tires but does this sound correct?
Thanks

Phil

 

Yes it does. That's what I would roughly get when I had my SRW's at those speeds. That's not bad all things considered. You pretty much answered your own questions too. Most guys getting better mileage than that are driving 55-60, or have 03-04 trucks, or 2wd.

 

2200 in 6th at 70mph ? You have a 4:10 rearend.

I get same speed and rpm but with 15mpg, I'd give an arm to be able to get 18.5mpg

 

thats pretty decent I would say... About what I get on a good day with no wind!!

 

Thats about right for your truck.

 

With my auto and stock tires I am only turning about 1900 rpm at 70 and I usually get 20+ if conditions are favorable. I know that my mileage drops significantly when I exceed 2000 rpm. At 2200 rpm I'm doing just over 80 mph and my mileabe is around 17+.

 

Well I'll just be happy with that then. And I have 3.73 gears and with the stock tires I was running a bit more Rs than that.

Thanks again all.
Phil

 

I have a 6 spd too. I am still running the stock sized tires and my freeway mileage is less than what I get running 50mph on 2 lane state routes. My RPMS at 70mph are about 200 higher than yours. I did notice an increase in mileage when I bought and loaded the SMARTY. SO you may want to try a programmer of some sort if you are looking for better fuel economy. Don't expect to jump to 25mpg. But you may see 20mpg if you can stay out of the throttle. I have gotten close to 21 on one tank but typically average 19mpg. Weather & temperature seem to affect mpg also. Just some food for thought.

 

That is good mileage. I have a 4.10 auto with 34inch tires and at 70, in good conditions I usually get around 17 or so. Be happy.

 

He has the G56 which has lower gearing than the NV5600 and 48re. That is why he is running those higher rpm's. IIRC, there was no option for 4:10 gears with the G56 in the 2006/2007 5.9's.

 

You're right.

 

Averaging out to 18.5 is pretty good. I've got a spreadsheet where I've calculated my mileage since the 2nd or so tank full. My lifetime avg is just a hair better than that at about 19 mpg.

I've got a high at 21 mpg when I went to a reunion and drove about 150 or so miles at about 45 mph on a good road. The rest of the tank I drove as I normally do on my normal routes.

I have found that I get better mileage when I keep my rpm around peak torque (this is expected). I can run around turning ~1200 or so rpm at 40~45 mph in 6th and get worse mileage than running 40~45 at 1600~1800 in 5th. Running in 5th too provides a minuscule improvement in efficiency by not running through gearing.

 

I'm getting 18.5 to 19 mpg pretty consistently at 2K rpm's, 65 mph, with my BFG 35's. I loose more gearing up to speed fast, better gaining speed going up slow.

CD

 

I drove my "new" truck to Denver last Saturday. Up I-25, and then over to Broomfield. 75-80mph most of the way. I got 19.5 on the overhead. Good enough for me.

I keep a general track of what my vehicles get. It's a good way of picking up problems early. When mileage drops, there's a problem. But I don't really worry too much about what that number actually is. The vehicle will get what it gets. Since I generally don't beat up the equipment anyway, there's not much I can do to improve the situation.

I looked at companies like Quadzilla and Hypertech. By comparing their claimed mileage gains against the cost of the tuner, it would take me 4-5 years to break even. Sooner if the cost of diesel goes up a bunch. Assuming their claim is correct, and nothing bad happens.
For me, it's not worth the trouble.

 

Final drive ratio might be hurting you, but a stick puts more of the engines HP&Torque to the ground ,dyno tests prove it, so as result mileage should be better, unless your final ratio is killing you. An auto might get better mileage in traffic though,less time between shifts than with a manual, but you'd have to do a lot of shifting for that to add up.