My sister has an 05 2500 4x4 hemi that she has towed some very large gooseneck horse trailers with many times. She has even towed into Colorado before with the big trailers. Gets bad mpg but handles everything fine.

Remember the early cummins trucks only had 160hp and there was one ton trucks with only 200hp gas motors. My dads old 80 crew cab dualy with a 360 towed a fully loaded enclosed trailer and a bed full of gear down the road at 70mph. I don't see how the extra 100 or more HP from the hemi is going to make it tow less, sure to might turn some more rpm but nothing it's not designed for.