Car advice- 96 cavalier 2.2L?

Hello, I have a 96 2.2L cavalier. I have had the trans flushed, coolant changed, I do 3K oil changes with castrol, replaced the plugs, fuel filter and air filter. It has 78K on it. It used to stall on random on me quite a bit, but now rarely does it but sometimes. It also occasionally bucks/hesitates on me. No engine codes and all hoses seem to be clamped down. I've taken it to a mechanic twice and no diagnosis. Should I get a fuel system clean done? Could it be some kind of gasket? Could it be the plugs? (I used autolites but they are the AC Declo equivelant) Thanks!
The coolant guage is never out of the middle area either