My 2001 Chevy 2500HD CC pulls my 32 AT just fine is well under towing capacity. It's about 10k on the trailer. I have the 8.1/allison. I would go with a duramax or 8.1 gasser. The 6.0 does not have enough torque enough in the right rpm range for towing and you can't get the allison tranny with the 6.0.