Rev hang? RPM increases on gear changes.
 

My engine recently has been "rev hanging" or increasing RPM by a few hundred when lifting off the throttle to shift up or down. It happens when shifting more than 50% throttle above 3.5k. Sometimes makes downshift rev matching inconsistent as revs rise too high. I read that this is an emissions issue programmed into the ECU. By keeping the throttle slightly open it reduces NOx. I'm not sure this is true with the 986 as this issue never happened before.

2000 Boxster S 106k miles 997 maf and throttle body installed 6k miles ago.

Sounds like something is sticking in the accelerator pedal or throttle body.