M2 with ISC-300 and Allison 3000hs 5.63 rear end

Hi there. I came over here from the hotshot page, I hope this is the right place.

I just picked up a single axle 2010 freightliner M2 106 with a Cummins 8.3 ISC-300, Allison 3000hs six speed auto, and 5.63 rear end.

I plan to use it within the State of Arizona, but all over. My issue is with the high gearing, and this speck, fuel economy for the lifetime of the truck according to the computer is 5.5mpg.. it's got 230,000 miles on it and computer says it's burned about 42,000 gallons. I don't plan to be over 54k lb gross combined. There are some long grades and steep hills here in Arizona, as well as long flat roads.

I thought I would look into getting this rear end geared differently to increase my fuel efficiency but I did have one gentleman recently mention he had a similar setup that was getting 9 miles to the gallon and he thinks I'm losing fuel efficiency elsewhere.

With someone here help point me in the right direction? I bought this truck because it was super clean and it was a pretty good deal, but I'm worried now that over the course of a year I'll spend so much more in fuel I should have budgeted an extra 30k and bought a different set up..

Empty and no trailer on flat ground it runs 65mph at 2000rpm.

Any help is appreciated

 

none yet, the numbers are from the computer in the truck after laptop was plugged in. shows 230k miles and 42k gallons used

 

Don't know, i couldn't convince the guy with the computer to give me any printouts, and i don't have access to the software. It was a praxair delivery truck is all I know.

Just wondering if I can regear it, if that will help to mpg, or if I need to look elsewhere

 

Cool. Will do. Cab card just came in today, will put some highway miles on it. I really figured that 5.63 gears and 2000rpm at 65mph instantly meant poor fuel mileage.

Will run it for a bit and see. I'll resurrect the thread after some miles

 

Awesome. Thank you for this insight