I'm on my 6th Duramax/Allison truck, best stock combo I've ever had.
20+ mpg in the H2 and could tow 2 more H2s behind it.
Allison has a lower 1st gear and the downhill braking plus 2 pto mounts (great for hydraulic winch).
This motor has more torque at 1000-1200 rpm than any other GM motor makes at any rpm.
Duramax/Allison H2, it doesn't get much better.
Also for the racers a Duramax p/u truck has run in the 12s quarter mile.
It had turbo help and propane injection.