[71GMC_3/4T]

The interior light has clickers toward the center. Push in on the sides and pry it out. Chances are you will crack it if it's original. The reproduction ones don't seem to fit right, but they will work.

You should be able to pull the screws out of you exterior light, then there should be two more screws holding the chrome housing to the cab. If you're having problems getting the lens part off, it's probably the seal that's still stuck real well. Do it on a hot day and pry slowly, it should come off. Start with the end, not the middle.