Yode, just a wild thought here and i wouldn't suspect this is the problem but . . . have you checked your lower ball joints since the install (or did you replace them with the lift)? Again i wouldn't attribute a "thud" or "cluncking" noise to the LBJ's nevertheless, since you haven't yet pinpointed the noise, it's something else to look at.
BTW you should really replace those anyway when you lift, if you haven't already. i can tell you from personal experience you don't want to drive 'em til they fail. If it were me in your shoes i would replace the LBJ's w/MOOG's before taking the lift back off. If that doesn't solve the problem and you decide to take the lift off anyway then you've simply upgraded your LBJ's anyway; and since DC only replaces their recalled LBJ's w/another cheap product the MOOG's are a good way to go.
Good luck & hope you don't ditch the lift.
