First off, never go to that body shop for anything.
There is a lot of stuff that can adjust doors on these trucks. As stated, the hinge pins are toublesome. But it sounds like either your hinge pins are sloppy as sloppy can be or your door is mis-aligned.
There are adjustments on the hinge bolts themselves, there is adjustment for the striker on the back door post, and there is adjustmenmts for the locking mechanism that is in the door.
Your first order would be to align the door to the body, IE hinge pins or hinge adjustments. Once that is done, then the striker and locking mechanism can be adjusted to each other.
This takes time and patience. So do not think you will get it perfect the first time.