22 WRX overboost issue

Hi all! I have a 22 WRX that was tuned by a very reputable tuner. (Didn't tune myself cause it's still a newer car and I'm not trying to experiment with it yet lol) The car has been great with no real issues. However since the addition of a downpipe and new tune, I have been having issues with the turbo overboosting. Tuner says the highest boost target in my map is 19.1 psi, however gradually rolling into the higher rpms in 4th gear and above I've seen peak boost as high as 27 psi before letting off the throttle. it climbs regularly into the 20-24 range and I just let off to keep it from climbing any higher. I would think he would've incorporated a boost cut into the tune, but that's another story. Tuner told me he has never seen this boost creep behavior before on this platform. Am I missing something here? The car has electronic wastegate control. Wastegate issue? the only other thing I could think of was the IWG not flowing enough exhaust gas through it with the wastegate fully open that keeps the turbo spooling and boost climbing. However this car only made 317 whp/ 389 WTQ on a dynojet so it's not a very high horsepower car. This platform has been regularly making higher power numbers on this stock turbo, and I haven't heard anybody having an issue with this. The only other thing I could think of, I did do all the mechanical work on this car myself, is it possible I made an error that is causing this overboost condition??? I'm stumped. For reference, modifications are ETS Intake, Top mount intercooler, charge pipe, downpipe, single exit catback, and air oil separator.

Jason,

If you post a datalog we can see if it's tuning related or not based on the wastegate position commanded and final, TD boost error (along with typical monitors i.e. RPM, MAP).

The feed forward and PID tables for the electronic get may simply need adjustment.

I agree, there should be throttle and fuel cuts set up to occur before 27 psi, but that's something to chat with your tuner about.

For what it's worth, I haven't seen one boost creep either, but there may be a mechanical issue.