I'm having a simular problem. I had my engine replaced 2 years ago. Now, from time to time, while accelerating (usually in 2nd or 3rd gear) my car will start to sputter and hesitate. RPMs stays steady, not shooting up or falling down. I recently had my fuel pump changed, and my fuel filter replaced too, but it is still sputtering. It seems like it happens more on wet, humid or cold days. Oh and I have had this car for 7 ears and replaced the Catalytic Converter 3 times. I have a 2001 Camaro V6. Any suggestions?