98 gmc jimmy 4.3 wont run more than 4 sec

hey out there,
could somebody please help me?
i have a 98 gmc jimmy than won't run more than 4 seconds (if it will start at all!) it is driving me crazy:screwy: i have put a new fuel pump,distributor,rotary button,computer,coil,new plugs,and i cant even remember now. i know that i have put in over 700. 00 in parts and still nothing except the fact that it is pumping gas into piston holes.please help