1997 Oldsmobile Cutlass Unsmooth engine at 2300 to 2500 RPM

My car when going about 60 mph or between 2300 and 2500 rpm acts like it is spitting and sputtering along. It almost seems as though it does not want to downshift. Sometimes it starts right up like a fuel injected car is supposed to and sometimes it has to be cranked and even push slightly on the accelerator pedal. I have noticed when reving the engine up if you get it to roughly 4000 rpm it will cut out and drop 500 rpm and then go right back to 4000 rpm. It will cycle like this a long as you hold the accelerator at that place. Might be getting to much air or not enough. Almost like it has a govner like my lawn mower. I have not hooked it up to a computer and the check engine light is on. Only 144,000 miles, wonder why? LOL Wondering if any one has any idea what it could be. I have replaced the fuel filter and the fuel pump. Just looking for some ideas. Hopefully it will be a simple fix. Thanks for the help and sorry about the spelling. Kyle