No power

I have a 1997 Cavalier and every time I try to accelerate especially going up hill it seems like its not getting gas and skips but if I let off the gas and then press it again it is fine and also when I slow down to make a turn and start to accelerate it like it has no power. I have recently replaced the fuel filter and thought that had solved the problem but the check engine light and the ETS off ligts keep coming on periodacally. They'll go off for a day and then come back on. I was going to replace the spark plugs and wires to see if that would help or I thought maybe it might be the oxygen sensor. Any advice would be much appreciated.