New hinge pins and bushings should fix you right up. A set of them will run about $25 at a GM dealer.
I've had to do them on a '90 one ton dually,'98 Z-71,and a '99 S-10 Blazer.
Its possible to replace them by yourself,but someone to hold the door steady on the jack while you replace them makes things a whole lot easier.
One last thing,head to the nearest NAPA and get the right tool for the job,again it makes things much easier. Its called a GM door hinge pin tool or something like that. Its also about $20.