When should you suspect TR related to pacemaker lead placement as a cause of RV dysfunction rather than pulmonary HTN or other etiologies for RV failure associated with tricuspid regurgitation?

It would be patient-specific but would need to include RHC to rule out pHTN (of any group). That should point you in the right direction. I suspect this would be pretty rare and would have to have very severe TR.

We know there is a magic amount of slack to put in the RV lead to minimize TR, but this...

This scenario comes up not infrequently. Sometimes intracardiac echo or TEE could be helpful to see if the RV pacing lead is going through the tricuspid valve leaflet or tethering the valve open. The best way to prevent perforating the tricuspid valve leaflet is to prolapse the lead across the valve...