It,s a 5 speed manual, can only get to 3100 rmp when the car dogs out. New cat, tps, mafs, fuel and air filter. What else should I be looking at?

What is your question?

The car has been doing this off and on for about 6 months. The check engine light will go on after a hard start. I will be driving it and have to shift @3100 rpms or else it starts to bog out. I have replaced the cat and 02 sensors, the fuel and air filters along with the fuel pump, the throttle position sensor and the mass air flow sensor. What codes am I looking for to get me in the right direction. I love my little car, it's been a good runner, but I just can't keep throwing parts at it that doesn't fix the problem. Should I be looking at the vapor canister, egr valve? Any help would be greatly appreciated. Thank you in advance.

What makes this problem better or worse?

The problem comes and goes. The check engine light will just go off, but now it's staying on.

How long has your 2003 Volkswagen Jetta had this problem?

On and off for at least 6 months.