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The Megajolt Lite uses crank position sensor (CPS) for static timing and the either Manifold Air Pressure (MAP) or Throttle Position Sensor (TPS) for load - TPS in your case. If you lose MAP or TPS or the ECU fails the system defaults to the static timing firing at 10 deg BTDC (limp home) providing the CPS is still working, if the CPS fails you won't get a spark at all.
Tacho can be taken from either the ECU (this is a 5 volts so mostly for modern gauges) or the EDIS A & B drives to the coil pack (this is 12 volts for old Smiths RVC type gauges that were fed from the dizzy and requires diodes to prevent x2 over reading because of the 'lost' spark); loss of tacho during rough running would indicate to me that your tacho is being fed from the ECU.
The rough running/poor performance could be because that you're losing advance, ie your engine is running in EDIS default 10 deg BTDC, which would indicate a TPS sensor or ECU fault
I'd be looking at the TPS, it's wiring or the ECU wiring. It was/is possible to buy the Megajolt as a kit of components so dry joints on the PCB might also be worth looking at. If you disconnect the ECU main connector this will force the EDIS into default and you will get the symptoms as a way of confirming the theory.
Tbh, mine was pretty extreme, not quite anti-lag but getting close to sounding like it...Along with a gunshot of a flat shift. Potentially made worse but addition of boost.
Signs were that the idle just rising, and rising, every few drives. Until it became ridiculous at which point the culprit was obvious.
Swapped them out and not had an issue in the two years of driving since.