Traded my 2006 Sierra 2500HD 6.0 V8 for the Allison/Duramax. Super truck. I was amazed how much better the ride is in the 2007 Sierra Classic. Duramax/Allison combo a real delight to tow with. The Allison 6 speed works incredibly well with the Duramax to couple all of that torque to the ground as well as assisting in stopping the whole load. Torque comes in at about 1500 RPMS and this thing launches like a rocket. Great fit and finish. I researched all other diesels and I'm happy I stuck with GMC.
Duramax/Allison combo. Ride and handling excellent. Anti-lock braking. Heavy-duty construction.