Truck wont start need help

I have a 2001 chevy 1500 single cab and short box
4wd with the 4.3L V6 in it in an automatic
transmission. It's got about 77k on it and the time
I've had it it had been known to stall out (not very
often) when I put it from drive to reverse it takes it
a little more effort to start than normal once it
does so anyways it happened to me again and this
time will not turn over it's got plenty of enough air
and spark but no gas. I have put gas in the throttle
body and it starts up but stops running once it
uses up the gas in the throttle body. I have
replaced the fuel pump and checked the relays and
fuses and all are in great shape. I really need help
any thoughts?