I am considering swapping a DANA 80 into my 2003 2500HD Duramax/Allison w/2WD. I have a free flow exhaust, low resistance air filter, and a Banks Ottomind tuner. I don't tow much so I want to do swap to get the 3.31 gears avail in a DANA 80 for mileage. My truck turns 2100-2150 rpm at 70-71mph. I would like to get the engine rpms to 1900 to get better economy. Any pros or cons about the swap. I realize retaining the stock disc brakes is going to be a challenge.

33"tires will put you at 1800-1900 @70 and cheaper
might need a leveling kit

i would say tires would be way cheaper. if you get the same size tires all the way around, you may find you dont need a leveling kit.

Nvrmnd