Internal balanced..what damper do I need

Dampers are designed to damp vibrations at a certain range of RPM's; that range all depends on at what RPM's things like the TC or flywheel/clutch mass wants to set a twisting vibration along the crank in conjunction with the rotating masses inside the engine; that resonance is excited by the engine torque 'pulses'. But having an intentionally imbalanced damper or TC/flex plate on an internally balanced assembly is not about the damper doing its normal job. It's about having an incorrectly weighted/imbalanced rotating 'thing' at one end of the engine or another, without the opposite internal imbalance, and it would be hard to say at what RPM's the vibrations will show up for this unbalanced combination.

And yeah, it surely could be some sort of low RPM misfire or uneveness in combustion, but the OP needs to fix the situation if he has a 360 damper, TC, or flex plate on an internally balanced assembly.