Did your cat swap solve your 'cutting back' issue?
I had that on the mk4, seemed like MAF had hit limit and was sort of going into limp mode?
Release foot, wait a second, then you could plant it and be back at full boost again?
Mine was peaking at 22psi, but I was only running ko3s, on a ko3 map though.
Standard injectors and MAF though so I couldn't have been anywhere near 235hp/188 g/s?!