Looking at new style 07 GMC 3500 have questions

[PHS79]

My father is looking at trading his 05 F350 DRW ext.cab, FX4, power stroke/auto in on a new body style 07 GMC 3500 DRW, ext cab, 4X4 (with off road package) Duramax/allison. His F350 has been a great truck, no problems at all. Just the that fuel mileage went to heck after the PCM got reflashed about 15,000 miles ago. He was getting 16 mpg running empty and now he is down to 11-12 mpg.

 

He just has a couple of questions about the GMC's before he does order the truck. He has been told by 4-5 people that thier 2500HD 4X4 Duramax's are getting 18-19 mpg running empty is this right?? What could he expect with a dually? With the manual shift on the Allison will it hold 6th gear and not downshift on a hill? Or will the computer still shift it out if needed?

 

Also is there anything else that he should know about?

 

Thanks alot

Paul

[KMT15]

Ive only got about 1600 miles on my dually so far (mainly just going to use it in snow and to pull our boat) Im hoping its just b/c the engine is far from broken in, but empty I was averaging about 14mpg or so. If I set the cruise at about 65 and reset the MPG thing, it would stay about 15-16 depending on how level the ground was. Didnt notice much downshifting either, even on some hills. I read a review of the big 3 diesels on I believe Edmunds.com and they said the 6 speed allison is by far the best trany and rarley shifted around while the other two did

[whitesnake01]

He has been told by 4-5 people that thier 2500HD 4X4 Duramax's are getting 18-19 mpg running empty is this right??

Fuel consumption depends on so many variables that it is hard to tell. In my case, I get about 21mpg on the highway empty, on mostly flat highways. I have stock 245/75R16s. As long as you stay below 1,900rpm you're good. For suburbia driving I get around 16-17mpg in the winter and a bit better in the summer. Towing a 8,300lbs trailer I get 12.5-14mpg depending on road conditions. I do not drive with a lead foot.