Forget the sticker in the door jamb, you threw that out the window when you took the stock tires off. The rating on the sidewall is for MAX load applied. You don't have that much weight on them. What I've always done, which is a tad easier if the tires are new cause you can watch the nipples, is just make sure you're getting a flat contact patch. Every truck is going to be different because we all weigh in different. The actual tire is going to make a difference too. 20psi is probably pretty close. Just watch how the tires are wearing. If the are wearing a more in the middle, take a little out. If they are wearing more on the sides of the tread, put a little in.
In my old Toy, '95 ext. cab, sas, 35's, I ran 20psi because the truck didn't weigh enough to push the tire down for a good contact patch at anything higher. I ran this everywhere, city, highway, whatever. If I had a real heavy load that I was taking for a decent distance, I would air them up accordingly.
In the Blazer, with 350/465/205 on 36's, it weighs a little more to help "sqaush" them down and I think I have them at 22psi, but I haven't done a lot of driving to determine where they need to be. It may go up or down a couple psi.
edit: flat spotting isn't going to hurt anything, they'll smooth out in a few minutes of driving.
