Mine is a Chevy 3500, so smaller than yours, but before I bought it, I went to the local Chevy dealer and he said it was too big for him, but sent me to the GMC truck shop and they have done all the work since.
I had the check engine light problem last winter, and the Chevy garage in AZ suggested the new gas cap and turned the light off. It soon came back on, so I bought the cap and it went off for about a month. When I got back to ND, I took it in and it was a minor leak in the exhaust system that they fixed under warranty.
So, my experience has been quite different. It depends on where you are I guess.