98 Buick Regal GS has a miss?

My car idles fine and runs great until about 30-55 but then it will start to miss or surge. It runs great at full throttle or even half throttle. I changed the MAF sensor, cleaned the throttle body, checked the injectors, checked all plugs, wires, coils, and I put some alcohol in the gas just to make sure it didnt have water in it along with some injector cleaner. What could be the problem?