When i start my truck it runs for 2 seconds and shuts off. I`ve changed the spider, checked the fuel pressure and its good, changed spark plugs and wires still no help. What could be the problem?

Most fuel injected vehicles no longer experience vapor lock, since fuel circulates continuously thru the fuel rail and back to the tank. More likely, you have an electrical part which gets hot once you shut the truck off. You need to test for spark to the plugs, and also correct fuel pressure when it fails to start and see which is lacking.

Maybe a problem in the fuel pump circuit. Check fuel pressure with engine off, and key turned to on, not start. If no pressure, diagnose the pump circuit at the fuel pump relay. One terminal for the relay would be the power feed for the pump. The engine computer signals the relay on for 2 seconds with key on to prime the system, also signals during engine cranking.

I saw what you replaced, didn't see any testing? What testing have you done? Make sure battery has a full charge?
When the problem is ongoing, have a helper crank it, while you check for spark at the plugs. If spark everywhere, use a gage and check proper fuel pressure. Also, check fuel injector pulse. Any applicable trouble codes?
If you have the spider fuel system, that system is noted for problems.

It possibly could be the alternator.

If you replaced the injector after the plugsthey may be fuel fouled.Pull the plugs and clean them.(you can sandblast them,or use a method I used to use-shoot a little starting fluid on them and use a lighter to burn off the contamination of too much fuel).I can't believe GM kept using this stupid design so long-I remember nearly new Vortec V6s with this same problem in the '90s.

check your ecm-ign fuse.if it is ok check to see if you have power to your spider injector.if you have power, you either have a bad computer or a bad connection between the computer and the inj.do you have spark??.if you have no spark check your ign module or bad connection at the ign module.i have seen that before.

I know this may sound crazy, but I had the same problem on mine.. But check your fuses.. I believe it's ECM 2 .. that fuse also runs the fuel pump...I really dont know how its tied into it, but it is .. Good Luck..

Will it run for a short time if you squirt some fuel into the throttle body? If so, then concentrate on the fuel delivery system. Fuel pressure at the test port on the fuel rail should be at least 40 PSI. If not, look at the fuel pump, the pressure regulator, and the fuel filter.

Have you changed the fuel pump yet?I had the same exact problem.I replaced my fuel pump with an AUTOZONE PIECE OF JUNK fuel pump.That pump lasted almost 2 days.The second day i had it the truck didnt want to start but it did and it ran like ****,and when i put it in gear it ran as long as I didnt touch that gas pedal.You could go get a fuel pressure test or just replace it,your call.You might want to check your filter too but im sure its the pump.Good luck

I would say the car is not getting any fuel. you could try replacing the fuel filter which is cheap. It could also be the fuel pump which is probably in the tank.(try tapping the gas tank with a hammer lightly) If the car starts then it is probably the pump. The last thing i think it could be is that is isn't getting any spark. Take the spark plug wire off the plug itself and put a screwdriver in the hole and make sure it is touching the metal part of the plug. Have someone try to start the car and hold the screwdriver near a piece of metal, if you see a blue spark then the car is getting spark, if you see nothing then you probably have a bad coil.