Originally Posted by 83hurstguy
I tow with a 2010 Express 3500, has L96, 6 speed, 3.42 rear. I have 75k miles on it now - the engine piston slaps cold, it's susceptible to breaking off exhaust manifold bolts, but the core engine itself has been great. I just changed oil and it hadn't burned any over the last 3k miles; trans fluid was changed around 55k with GM stuff, fluid is still clean.
Tows open trailer with car (5000 lb) like nothing is back there and rides great, probably gets 11-12 mpg on highway with the open, more like 15-16 mpg no trailer. Once I went to a 24 ft enclosed (probably towing between 8-9k), it did okay, if you were pulling up hills you just had to get used to hearing RPM, and it would get right around 8.0 mpg. Since I don't have a great rear gear ratio for towing like the pickups, I just lock it in 5th gear and let it kick down to 4th or 3rd when needed.
Best change I made was getting it professionally tuned - in the vans, GM never let it go into power enrichment mode (had it effectively locked out) so it was always trying to pull at stoichiometric (14.7:1ish), the torque converter locked in every gear (tuner disabled for gears 1-4), and the timing tables were really soft based on intake air temp, so it was effectively always pulling timing. It feels like it picked up 30-40 lb-ft from the tuning, pulls hills way better, acceleration is great, and now I'm getting just a tick over 9 mpg towing the exact same route with the same trailer at 70ish mph. I do typically use premium fuel due to the tune (don't need it around town unloaded), but it's worth it due to the power and economy.
The sad part is that the rest of the truck will have issues with everything else (wiring, accessories, evaporative emissions control system, rust) long before the powertrain gives up.
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