car will run but only when it wants to i have replace fuel pump on 1998 Oldsmobile Bravada

the first time would not run discounted fuel filter was not pumping fuel check all fuses relays replaced pump car wouid not start then it started ran ok started 20times sat over night would not start played with it it started same thing agian some thing shuts down pump found some thing is shuting fuel pump off would oil presure gage shut pump off the gage does work seems the check motor light does not come on works when you turn key on i have checked all fuses @ relays replace coil crank sensor battery truns over ok

Have a mechanic check fuel pressure to see if it bleeds off quickly when engine is switched off. Verry possible you have a "fuel spider" (injector) problem.
It's not a possible but a probable.
1 more answer
check your fuel pump relay and also check for codes