do me a favor and try these 2 scenarios:

1. remove one of the charge pipes and give the car more throttle and see if it'll buck as it did before. This'll distinguish whether it's a boost issue or not.

2. remove the missing link (ML) and blow through the bottom o-ring'd part on the ML. if you can blow through it, it has a bad check valve, hence, your issue is a bad ML. pic shown for reference (bottom is the o-ring'd part i'm speaking of)



you can try #2 first, easier to test