92 c2500 4X2. I am trying to reglue my headliner. I can not figure out undo the plastic that holds it in . I can not find any screws and I am pulling and twisting without success. What is the trick?

If yours is like mine was, then here is how it goes.

Remove the "oh-[censored]" handle from the passenger side above the window, the screws are hidden under a plastic cap on each side.
Remove the sun visors (3 screws each) and don't loose the little metal clips (you'll find those after the liner is out).
Either remove or just loosen the plastic trim above the door windows. pull down and wiggle to loosen from clips. you'll have to get a little rough but don't break it. They are just metal clips that are screwed to the roof and they clip on to the plastic trim.
As for the rear piece of trim (where the dome light is) I didn't take it out but it might make things easier for instalation if it is gone.
At the front of the liner (above the windshield) there is (i think) 2 plastic clip things that almost look like velcro. Don't treat these like velcro or you will break something (I did). With my experience here wich is not much, I now think you should try to un-clip or whatever these plastic things from the roof, instead of trying to remove the liner from the plastic tabs. You might try an interior panel puller tool, I really don't know about this one, you'll just have to play with it and see what you think. After all of that, with a little twisting and pulling and the liner should come right out. I had bad luck with the glue sticking, so I removed it again scraped off the glue and insulation from the liner board and put 2 coats of fiberglass on it. then I painted a rebel flag on the glass, re-installed it, and have been offered gobs of money to make another.

Good luck.