GMC Repair: 1994 GMC k1500 5.7 liter 4x4 with Manual Transmission, delco battery, ac delco

Question
Ok so this is going to be a long one. I recently bought this truck and have another that's a v6 same year. I'm pretty knowledgable when it comes to GM. The truck had a backfiring problem when I bought it. I have replaced the fuel filter, plugs and wires, dist cap and rotor,ignition coil, new delco battery, Pcv valve, air filter, throttle body gasket, map sensor and changed the oil. It drove just fine over the last 5 months with the backfire...although at times it would act up and other times it would not. After changing the tb gasket the next morning it started backfiring badlythrough the tb. When I leaned on the map sensor it broke idle. I drove it some more and the engine sounds great but it backfired so bad I had to pull to the side of the interstate. I got out and revved it one good time from under the hood and it idled down and shut off. I replaced the map sensor and it still won't start, I pushed started it and it ran for about one to two seconds and cut off. I have replaced everything with ac delco and am very frustrated, the fuel injectors are spraying fuel just fine and the fuel pump is working any ideas?

Answer
I would lean toward timing, or the timing chain. If it were me, I would go to TDC and check all your rocker arm torque and valves to make sure they are right, check the firing order. I bought a dodge dakota with a messed up firing order, and I did the same thing you did, and it had the same symptoms.

 Definately check the valves and timing. If that does not fix it. email me again.