that test takes the pickup out of the picture cuz you are directly triggering the ECU with the dragging as opposed to the pickup electronically triggering the ECU so with it sparking that points to the pickup as the culprit but what skews things is that the offender is acting up part time (from the heat) & that changes rapidly with electrical items (can come and go fast/randomly) so the coil or the ECU or the pickup could be what is bad but k.i.s.s. since we have changed the coil and ECU several times (at least!) logically as you noted it is time to replace the pickup (or dist). Short version: got another OE dist (or pickup from one) to toss in real quick