If you think it might be a crank sensor. Shotgun one on. I've seen a lot of funky behavior from a crank sensor.
My first happy time with one was my car would seem to hiccup once or twice a day on the highway. I couldn't duplicate it, wasn't until I was scanning it and saw that the run time counter had restarted when the hiccup occurred. Literally my car had stalled and restarted. Tach didn't go to zero, none of the "expected" stuff mentioned above.
I've also noted that on most crank sensors .. they are magnets and collect crap in between them.
