I have a 2004 Duramax/Allison set up with a programmer. I love it and love the diesel. But, the upfront cost of a diesel made me question buying one, and makes me question buying one again.
If I was buying a new truck, I would probably avoid diesel due to the emission stuff currently installed that do nothing other than restrict the engine. I also just heard due to some lawsuits, some of the programmers and other mods are illegal to manufacture now.
I would buy an older non-DEF diesel which I could remove some of the emission stuff. Diesel is made to last and pull. There is a reason commercial vehicles use diesel engines. The lifespan is tremendous with maintenance. I saw a mention of gas being 400hp and 400/ft lbs, which is good, but diesel is massive torque.
If you want a heavy trailer and plan on keeping the truck pony up the money and get a diesel otherwise go with a large gasser.