You're planning on loading your ONE TON pickup to over 30k? :badidea: If you wanna play Billy Big Rig, buy a big rig.
We arn't dealing with a 1 ton here, the 3500hd's were rated between 14k an 18k, and BTW take a look around most hot freight guys are set up for 36k gross 12k on the truck and 24k on the trailer, and that is with a 1 tons.. I have a good friend who puts 100k a year on a dodge 1 ton hauling cars, due to the difference in fuel consumption he makes as much as he did with a semi. There are times when small works better..his current truck has 350k on it and no major issues.
I didn't miss it at all. I had the same idea a couple years ago, and I tried it. 12V Cummins, SM465 manual (1:1 final ratio), and 3.42 gears with 37" tires. With new tires I turned 2050RPM at 65MPH, and around 2350 at 75. In theory, the less paras[/B][/B]itic drag with no OD should have let me get better mileage. In reality, the guys with heavier Dodge trucks, no front hub locks (so, more parasitic driveline loss) and OD transmissions that turned a mere 200 fewer RPMs got better mileage than I did.
37" tires, ya had a set on my first gen dodge went from 22mpg to 13mpg.. the rolling mass is huge.. not to mention the wind drag. My 3500hd has a smaller frontal area than any dodge i have had and with tall skinny 19.5s it rolls alot easier. and do over 20mpg at 8500lbs empty..
As it turns out, engine efficiency at higher RPMs drops much faster than the bit of extra loss caused by OD operation. Ideally, the engine gets best fuel economy when operating at it's torque peak, which is 1600RPM for the Duramax. With a non-OD trans and 3.31 gears you will need 44" tires to get in that RPM range at 65MPH. If you run an FSO, which has .78 OD, and the same 3.31 gears, you can get in that RPM range with 35" tires. Your current 4L80E is even better: 3.31's and 33" tires nets you 1642RPM at 65MPH. Unfortunately, it has a mediocre (for hauling) 1st gear ratio, and a terrible reverse ratio (backing a heavy trailer with a 2.08 reverse gear blows - BTDT). And it has nowhere near the GCW rating of the other transmissions were discussing. Although, interestingly, you disparage the Ally's mere 30k rating rather than in the much lower rating of the 4L80E you're running now
Then explain why almost none of the medium duty trucks are specked that way, they almost all have non overdrive fullers in them even the over the road ones they run high gears and a direct trans, the only ones I have seen with FSO's are the Fedex expediter trucks and the reason for them is they run 70+ all the time...
The Allison has a .61 OD, so you no longer have to run 3.31's to get the low cruise RPMs. You get there with 4.10's and 32" tires, which is what you have right now. 1st gear is 3.10, reverse is 4.49, so taking off and backing up is much easier.
Then there is the issue of bolting it to the engine and making it work. Ever looked into what it takes to adapt a Fuller to a Duramax?
After a reality check, you will find your best options are A) Stick with what you have now, B) Swap in an Allison, or C) Swap in a ZF 6 speed.
