Ya say it would only start in neutral? You might have an issue with the neutral safety switch. Me if there was any question of the relay being bad I's just throw that part at it. Its only 10 bucks at autozone. If you dont have a repair manual for that truck with as old as it is and all you oughta get one. That will give the diagnostics for each system.

 

Click on his thumbnail image......................

TSB = Technical Service Bulletin
MLPS = Manual Lever Position Sensor (like a neutral safety switch)

 

Make sure your preferences are set to show images in posts & signatures. Here's a fairly complete list of Automotive Terms & Abbreviations.