Truck runs for two seconds an shut down i changed fuel pump an filter and it still shuts down but it only stay running when i put gas down in the throttle body i had a 1996 chevy 1500 i was wondering can the fuel regulator from a 1996 chevy 1500 fit in a 1998 chevy 1500 z71

Anti-theft system problem ? Is there a SECURITY light on the instrument cluster that stay's lit ?

At this age the pump would be a good bet. How many miles/years are on the current pump ?

Hi James:
Since it starts you have spark so I'd be looking at the fuel delivery end of things. Most of us pump the gas pedal so that would prime the motor (accelerator pump) so there's fuel in the carb. I'd be looking at gummed up jets as a possible and trying to clean up the carb.
Now, if you tell me it's a diesel I'll be completely demoralized.

Good fuel pressure from the pump is fine, at the pump. But if it can't flow constantly it WILL shut down. Have you though about changing the fuel filter? even a dirty fuel filter will allow enough fuel to the engine to allow it to run for a few seconds or so. When that little bit is gone, can't get enough to still run.

probably a bad fuel pump

I know its a pain but i would drive it with the fuel pressure gauge on it and see what fuel pressure is at when it stalls also scan it for dtcs and if none found suspect crank sensor

Really

The 20 lbs wasn't a clue

You need 60#

Replace the fuel pump

Fuel pump is bad. It still runs enough to get gas to the engine, but doesn't put out the pressure to keep it running. Replace the fuel filter with it.

check your fuel filter make sure its not clogged up you probably need to get a new fuel filter.

It Sounds Like A Fuel Supply Problem. Which Means It Might Be Your Fuel Pump. Check Your Fuse's And Battery Connections Before You Start Getting Into Dropping The Tank And Replacing It.. I Had A 94 mercury That Would Run In The Winter But Would Shut Off While Im Driving Down The Road In The Summer. When It Would Shut Off I'd Listen To My Car. Turn The Key On For 4 Seconds And Off for 2 and Have Someone Listening To The Gas Tank. The Pump Should Make A Constant Tone. If The Tone Changes up and down or if you hear grinding. theres your problem. a basic electric fuel pump for a car should turn on for 3-5 seconds and shut off when you turn the key on. NOT STARTING IT.