I have taken my GU back to (almost) standard. Only engine bits: exhaust plate and catch can.
I get a limp after a few minutes at 110 km/hr, no issues at 100 or lower.
Remedy is to back off for 1 or 2 seconds, then all good until next time. That is OK unless using cruise control,

Has anyone tried a hole in the exhaust plate, similar to the Common Rail models?
If it works, what size hole is best?

Help or comments welcome.