Why will my vehicle start and idle but when I try to drive it dies

**DO YOU HEAR THE PUMP** 'In a quiet environment'... Have a helper get in truck, close door with window up so the ding dong noise won't drown out everything else when the key is turned on... You go back and take gas cap off and listen close at the fill spout for the 'fuel pump' to start running when helper turns key on!!... (Use hand signals if needed)..Should hear a humming noise for aprox 2 seconds and then it should stop!!... **Do you hear the fuel pump**run for 2 seconds each time the key is cycled from off to on OR engine is cranked momentarily, then let off key.. DO YOU HEAR THE PUMP ?? To get the idea...try it on another 'working' Chevy around there close by if needed!!! Post your findings....