does the truck have a premium guage pack? or is it just idiot lights?
if there is an oil pressure guage along with a light then there may be 2 senders, one on top of the intake beside the distributor which is just the switch and then one mounted on the side of the engine near the oil filter which is the sender for the guage.
if either measures less than 2psi for more than 30 secs it will shut the engine down, so if one is defective it could be causing this.

checking the vaporizer as kevin and others suggest would also be a good thing to check, the symptoms you have lean more towards a fuel issue anyway but i just suggested the oil pressure switch/sender because they are known to cause problems.