Save your current tune to a PC / laptop

Then just change the waste gate duty table. I had the same issue on mine and had to take 7% duty out of it across the whole table to stop it hitting boost cut.
It's easy to do and as you're not touching fueling or ignition it has no impact other than dropping boost. Obviously if you're adding boost it becomes an issue but not removing it.

__________________
605whp
Quarter Mile in 10.9 seconds @ 135mph /217kph
0-100 kph 3.2 seconds