Originally Posted by GREASYHANDS
Sounds like a bad ignition switch. Swapping it out shouldn't hard with the proper tools.
Before you decide to throw parts at it check the connections under the power distribution center for corrosion. I have seen several of these trucks with similar problems, make sure to look for loose wires as well.
x2, check for corrosion, it's likely the ignition switch but peeking around is free! Good luck