Do you have a means of data logging ? if the ECU is commanding the dump you can fix things all day and still have the issue.
most common issues
--weak seals on the BoV .. VERY common on high mileage vehicles... TBH unless you grandma it around you should replace both at or before 100k for G&Gs IMO
--to much boost forcing ecu to dump boost
--bad boost solenoid controller, not opening the wastegates soon enough, forcing ECU to dump pressure out the BOV
--bad wastegate, stuck closed building pressure under even the smallest throttle forcing ECU to dump pressure out the BOV
--bad MAP sensor, bad high pressure, reading forcing ECU to dump pressure out the BOV
--loose lines on the boost solenoid controller.
--globs of oil in the boost lines, causing all sorts of weirdness
it is a lot to diagnose .. you might be better served to take it in ..