This sounds similar to what I'm having at the minute, fine boosting through 1st/2nd then change into 3rd and it starts juddering on boost then cuts out about 5000rpm and I get a loud pop/bang when I come off the throttle, I'm on standard ct9 with an adjustable actuator, boosting at .6 but as I get through the gears I've had .8, obviously wondering what it is but I'm also concerned whether it'll be causing anymore damage? When I bought my car my precat lambda was cut and a couple of friends of mine thought it could maybe be down to that, I have another waiting to go on but I was wondering if it could be fuel cut instead?