We have an 04 2500HD with the LLY Duramax and an 04 F350 with the 6.0 and I hate using the Ford to tow anything. It has only 150k miles on it, and I believe that we have put enough money into it to buy another new 350 at full price!
It has left me on the side of the road three times while pulling a lawn trailer. The worst part is, it's not even worth trying to sell it because we have so much invested into it.
As for my Chevy, I have over 210K miles on it and so far no major repairs. I regularly tow our 853 and our TB135 (not at the same time mind you) and average about 12mpg while towing.