I've had this truck for couple years just sitting it has done it since i first bought it and let it sit do to other projects. Well now Ive been working on it and I'm about start college to be a auto tech and I was wondering what would cause this to happen I've read on multiple sites from running to lean to jumping a timing chain tooth and so on and none have really have an answer to what it was so can tell me what they think it is it pops under load. Thanks in advanced for the replies and information.

 

If you feel like checking it , mark everything before removing the distributor and when removed check if you can run a straight piece of wire through the rolled pin that holds the gear to the dist shaft. If that is OK it would eliminate one of the possibilities of the timing changing .
Have you thoroughly checked things like the cap, rotor and connections.
Dirty injectors come into the picture also as does low fuel pressure.