This is not about my Camaro, but my '91 K5 blazer (350 with TH700R4). There's so much knowledge here that i thought to ask here.
I'm sometimes having a heavy vibration in 4th gear when lockup is on at light throttle action (so lockup stays on).
As soon as lockup disengage, the vibration is gone.
When it occurs, it feels like driving over a washboard.

I'm guessing my TCC is worn but i want to exclude possible other reasons first before pulling the trans.
TCC valve??
4th gear switch??
VSS or TPS ??

Check the secondary side of the ignition system. Ignition coil, cap/rotor, wires & spark plugs. Good possibility that a misfire is causing the issue.

RBob.

If i disconnect the TCC connector at the tranny the vibration never occurs, so it most certainly has something to do with the lockup system. Would a ignition related problem not also cause issues in other situations like moderate or heavy acceleration?