Torque converter affecting idle question

Is it possible that the vacuum advance is active?
If the primary butterflies are too far open, this can happen. Then in neutral/park idle will be high; and when in gear, as vacuum drops the advance drops out and the idle falls into the basement.

The transfer ports should be square to very slightly rectangular UNDER the butterflies. The carb has to be removed to set this. If the engine idle is too slow in N/P after this is set, then, either the idle-timing is insufficient. or the engine wants air from another source; such as the PCV or the secondary cracking screw.

If the vehicle is sluggish on take-off,and the timing systems are working, the TC may be bad, but if take-off is brisk, I imagine the TC is good. Take-off is the the first second or two from a dead stop. A faulty TC will also show up as a lazy motor ,in traffic.