Lots of circular arguments and chest pounding but more importantly:
Why?
The cost difference is minimal to move up to a 3/4 or 1 ton. Or are you saying you already have the 1/2 ton? (in which case give us the details and it's pretty easy to tell what the ratings are)
Diesel vs gas is a bit more complicated (and mildly religeous). Unless you are going to be doing a ton of miles or always in steep mountain terrain, one of the large gas engines will provide plenty of pull at a much lower up front cost. It's mostly a cost analysis at that point.