The BBK X is actually a real good piece. If you are having issues the inspect it and make sure its all good. If it looks good... I'm going with user error. Mine fit perfect every time and I had it off a bunch messing with the transmission on my 98.
No leaks, no issues, MIL eliminators used, made sure everything was properly plugged in and sealed and it sounds very good.
Also, plz no X vs H arguements, its been beaten to death. Power difference between the 2 is nil. X is raspier, H is rumblier. Pair the X with a straight thru muffler and the H with chambered. The BBK pipe that I had works similar to a MAC Prochamber and sounds good with both types.