265 Stutter/ weird behaviour over 5k rpm in 3rd gear

Start with its a 2014 265, stock as far as I know. Problem Im having is with 3rd gear above 5000rpm. 1st, 2nd and 4th gear no issues, boost on RS monitor says 1250-1300 mbar, but 3rd gear it climbs all the way up and eventualy says 1400> mbar (max on the monitor). Im assuming the car is over boosting in 3rd? Why?

Ive ordered an OBD2 scan tool just waiting for it to arrive. Until then anyone has/had this issue and what was the cause?