1998 Chevrolet cavalier ls, 2.4L engine, lack of power question.?

my 98 cavalier, dosent have the power its hould, around 4,000 rpm it stalls out, ets off and check engine light are on, we changed the egr valve, fuel injectors, crank shaft sensor, spark plugs, fuel pump, but are still having the same problem, and suggestions on wht it could be, the check engine light is on for multiple things which we have fixed already.....