My 1999 Mitsubishi Diamante truck won't latch what can I do to fix it

If you are saying the door will not latch securely, seek local body shop or mechanical shop guidance. You may have a misaligned door due to sagging hinges for example, or you could have a latch that simply is inoperative. It seems you have done as much as you reasonably can, so it's time to consult local help.