sounds like slipping clutch maybe its just on the edge and when boost hits hard it slips it and when you ease it on its just hangin on.
Ease it on then back off and stab it see what happens then i reckon itll slip
Funny thing re clutches. I've just swapped out my 3rd clutch in 3 weeks for later model Evos, a clutch in an RVR today and a gearbox in a IX on Monday ! Comes in runs ...