90 Tracker getting too much gas

I bought a 90 Tracker about 2 months ago. First week it drove great. Got good fuel milage. Second week it would take forever to get it started. Took it to my mechanic who said the computer was bad. Bought a new computer and it drove okay the first day. It was a little sluggish on hills though. Second day I made it half way down my drive way. Called my mechanic and he told me to unplug the connection going to the injector, try to start it with it unplugged, re connect it, and it started right up. Drove around all day. Next day, I didn't even make it out of the driveway after 2 hours of screwing with it. Now my mechanic says it's getting too much gas. We've changed the computer, plugs, wires, cap, and still it won't stay running once you get it started. I'm by no means a mechanic or even mechanically inclined. But my hubby and my whole family are and they are stumped. I've been told it could be the fuel pressure regulator or the throttle position sensor or that it's the computer. But my mechanic tested the ecm and says it's good. Any help for a poor stranded woman?

Check the fuel injector, fuel filter and fuel pump. :-p