1989 Isuzu Trooper Hesitation/Crank-Up Problem

I have a 1989 Isuzu Trooper 2.6 four-cylinder gas engine,ive been having what think is a fuel/electrical problem,a few weeks ago it shut off after filling tank with gas,my mechanic said that the Fuel Pump was bad so he installed a new one.About a week later while entering the freeway the exact same thing happened. So i took it back to shop, he checks it again and said that the new Fuel Pump was defective so he again replaced it with a second pump.Once again it shuts off,again he tells me,another defective pump. At this point im about to explode! We installed a 3rd pump of which is a re-manufactured OEM Pump. It was fine for a few days then it was cranking it was the next problem.It would start then stutter for about 30 seconds then once i start to drive it has bad hestiation,so I then replaced Oxygen Sensor,Spark Plugs,Fuel Filter…It cranked and drove fine for about 24hrs but then started the EXACT SAME PROBLEMS all over again.PLEASE HELP

Allen Ross,email:urbnlife2008@aol.com