Gas in oil

Well, if the fuel pressure reglator diaphgram fails, then fuel can get in the oil as you describe. On some engines, the regulator is under the intake manifold, so getting to it to check is not trivial.

This failure happend to me, but it was not as severe as you describe - the vehicle ran, albeit poorly. But gas-diluted oil is not good!

Except a 91 Chevy 1500 had throttle body injection, so the fuel regulator is in the throttle body assembly. We are assuming, because there is little info to go on, that the vehicle is stock. Also we don't know if after changing the oil and his statement "with the same resultit" means it ran for 30 secs and died, or ran for 30 secs, died, and the oil was way over full again. And the check engine light should come on when the engine stalls. If the injectors or fuel regulator were leaking that much fuel down the intake she'll suffer hydrostatic lock up, unless the pistons have holes in them, in which case she would never start in the first place. So we need fuel injection info, or carb and fuel pump info if its been modified. and further clarification of what "with the same results" means. If it started and died, I would lean towards gasoline that's gone bad and has with a ton of water in it to boot as a starting point.

Whitelightning

It is a stock 1991 chevy silverado 1500. When i changed the oil and tried it again the engine ran for about 30sec. and stalled just like before.

do you hear the fuel pump run when you crank it over now? just because the pump ran before doesn't mean it's running now... you have no idea when oil loaded up with gas. and you said you had to charge the battery after the winter was over....i worked on an 98 chev k1500 last winter, the fuel pump was just running to it' hearts desire even with the key off. it would run until i pulled the fuel pump relay. i put it back in and the pump was off. crank it for one milli-second and the pump kept running even with the key off. left unattended this would have gone on untill it dead headed the pump, killed the battery or burnt up the pump. now with your TBI and weak regulator or a leaking injector , over time,....just a thought.