I have a 1989 jeep wagoneer that starts then dies I replaced all the spark plugs and checked everything?

the car used to not start but I found that by putting gas in my pump and pressurizing the system through an outlet on the fuel injection rail I can get the car to start. The problem is that the car starts and revs fine and everything but after 30 seconds or so the engine starts to sputter and dies. the thing is that when it sputters If I take my foot of the pedal it returns to idle but extremely ruff and then you just watch the rpms go down slowly until the engine dies. I'm going to try injecting fuel injector cleaner into the fuel injector rail with my pump to see if that helps but I suspect that it may be the pump or filter. If it heps the car is an automatic v6 and this all started happening while driving up a hill. before that it ran smooth and fine and never quite. so I don't think its the computer seeing as it wouldn't have run before. also before it became this bad the car would run good as long as you kept it at a high rpm. there seems to be gas but maybe the pump is weak.