1999 GMC Jimmy car's engine is ok until it warms up

First, do you have a "check engine light"? It may be several things such as vacuum leak, throttle position sensor or the mass air. How long has this been going on? Please advise, it will help us narrow it down.

the light has been on for over a year. the accelerator problem has started a week ago as a slight stutter when i pressed on the accelerator. it would pause then i would get power.
i have had a problem that i failed to mention before. for about a month now i would start my car when it's cold and it would start ok. when it warmed up i would have to try to start it about 3 times before it would kick in and start. I blamed it on the ethenol gas i used a couple of times...Maybe this is related?

Your check engine light may have been on for a year, but whatever tripped the light may have worsened to the point of affecting performance. There are 2 or 3 sensors that could cause the symtoms you describe. With the information I have to go on, all I can do is guess at the solution, and guessing can get expensive. Please advise.

I had a computer check ran at the local auto parts store... showed a faulty forward oxygen sensor, so I'm replacing it this AM, as well as fuel filter, oil change etc. should this do the trick?

You're on the right track. If that doesn't do it, give us a holler back.