1999 mitsubishi Eclipse Spyder Loss of power, problem unknown?

my eclipse 5spd, non turbo 2.4 ltr, has a major loss of power, kind of like always lugging the engine, took it in and replaced the egr valve because it was sticking. Didnt fix the problem, they thought it might be the exhaust, But then they checked it and its fine. no place knows whats wrong. they say everything looks in good shape. car only has like 100k. anybody know what the problem might be?