'93 C1500 stall and backfire

My '93 c1500 with a tbi 350 will sometimes stall under moderate acceleration; the engine only has about 30k miles. There was also a time when the check engine light came on, I popped the hood and moved the throttle lightly and the engine stalled, I did it again and the engine stalled then backfired through the throttle body. After this the light went off and the engine seemed to function relatively normal. Also the transmission was slipping badly when light was on and went back to normal after light went off. Strange