ADDENDUM:
The haltech ignition module gave up the ghost and died last month. In hindsight I suspect this was gradually failing and the root cause for my troubles at the annual usa7s trackday. Facing a re-tune: upgraded camshafts were called for, and once installed the engine felt happier even before re-tuning.
After a long chilly drive yesterday (with wet return home) the car is once again running smoothly and better than ever!
Many thanks to Alex at Granite State Dyno in NH fitting me in before the snow this week :party:
Cams increased hp & torque by 20 points each; unfortunately upgrading driver quality will take more work.