I just bought a new 2500hd with 6.6 gas, last Thursday. Friday I pulled stock trailer with 18x 600lb feeders about 60 miles on interstate with cruise set on 70. It did just fine, It would hit 3000 rpm when it down shifted on the hills. I will be about 90% running around without trailer and 10% loaded trailer.

I think you will be fine, just might take some getting used to with the rpm's and less torque.

They rate the 6.6 gas at 401 hp, but that is at 5000 rpm, I not planning on hitting that mark.