Haven't had any problems yet on mine but I do work at a collision shop. Would suggest holding the door firm with your left hand between the outer door handle and window trim and pulling the top in with your other hand. Or another option would be to loosin up your door latch and bring it in and that should help. You can sit inside and shine a flashlight around the wheater strip and look where it's not as tight, still not working try taking off seal and pulling lip out more then seal back on. Hope it helps
I haven't checked on these mirrors yet but on most others, I just move the mirror lenses left right up in down and look behind in find the little clips holding it in and just unclip um using a skinny screwdriver.
Here's a picture of the tailgate handle I ordered, with the chrome and painted the rest to match. I also debadged the tailgate only left all terrain on right. Painted front gmc emblem, fender flares and fog light surround. Next is the mirrors.