If you've ever done this, you know the rubber gasket tends to want to fold over and/or buckle (some might say pucker) at the corners...and the lower corners with the more acute curves are usually the worst offenders. Hopefully you're the sort of person whose work just falls into place with never a bobble, but for many of us that isn't the case and the weatherstripping in the AD trucks never seems to straighten itself out over time. If you're installing new rubber, try this: pull the corner first downward from inside and out. Lock your index finger and middle finger of each hand in and pull the strip down and into the corner. Doing this you should see the buckle improve. Then once you've got the glass in place use as much hand strength as you can muster to once again pull the upward part of the strip up and toward the middle of the run and then to push the lower part of the strip out and toward the middle of its run, also. By doing this, you're trying to starve the corner of weatherstripping and push it toward the middle. On the rear windows (including corner windows), don't install the lock strip until you have the buckles worked out and move the glass and weatherstrip piece in/out a bit to help remove the buckles. The chrome-look strip isn't much fun to install. I'll post a couple of things I learned about doing that later.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end