I'm driving our new company truck, a 2005 Chevy 2500 dually Duramax from Sioux City to Las Vegas. I know it's pulling a heavy load and it has less than a 1000 miles, but I expected better than 7 mpg. Oofah. Our 2000 Cummins w/ 270k miles got 10 mpg pulling the same trailer.

And this Allison trans is making me crazy going up and down the mountains on I-70. It's upshifting+ downshifting nonsensically, and refusing to up and downshift. Basically making me nuts. It makes me miss my NV5600, where I actually got to choose the gear.

 

That's interesting. My mom's dmax can pull a 10k load without even thinking. Granted it only gets about 10 pulling it but it never has a problem finding the gear. I've never seen it drop out of OD unless it's a really big overpass (that's all we have down here ).

 

my friends d-max gets 6 mpg pulling a 35' toy hauler. my chevy crew cab 3500 drw vortec 454 gets 4 pulling 22500gcvw

 

In all due respect for the truck in second place.... I do not hear complaints from those hauling gross loads (25k to 30k) with them. They get 10 or so on pull. You should have it checked.

 

That's really low. In my non-expert opinion, I would think the erractic shifting of the transmission and the low fuel mileage are related. Probably a programming error with the Allison or something it the ECM. While I have not driven D-max's through hills like that, the ones I have driven have been very nice, overall.

 

I was a lil yesterday. Ran my snowmobiles ( yeah bout time i did this) down to the family farm about 200 mi away for storage. I have 3,polaris sleds and a 4 place trailer. Once i got there and hand calculated the mileage woofta. I wanted to weigh the trailer haha. I usually get 13-14 with her. Got 9 on the way down! which im not 100% suprised. Was driving into a 25-30 mph headwind. with gust up to 38 according to the radio. I knokw sometimes i had her floored just to keep my 65-70 mph. So that was sad. Hand calculated way back (empty) though was 22.6! Yeppie for that. but the camper we drove back has a 460? does that sound right? Its in a dodge chassie 1979 camper. Got 6 mpg. Ouch overall a costly day

 

No, was probably a 440. The Truck blocks were pretty stout, but the later ones had thiner castings. Nice thing was the later heads had hardened valve seats for unleaded fuel. Diesel is the better way, though.