2000 Suzuki Grand Vitara 4x4 fuel delivery?

I have a feeling that my vehicle isn't getting proper fuel delivery. When I start it up it, typically if it has already been running, it either kills or won't turn over so I stop turning the key, back off the key, and then try again pumping the gas pedal in which it starts. Sometimes it start but if I put it in gear it kills. I changed the fuel filter, but could it be my fuel pump? I live in central america and the fuel here is very dirty. Any suggestions would be greatly appreciated in what could be causing this problem. My engine has also been completely overhauled and I had the fuel injectors cleaned last year and changed the fuel filter last year.Car Repair Talk's forum.