P1391 is intermittent loss of crankshaft or camshaft sensor signal. The fact that your tach is bouncing around kind of backs that up. I would do a careful inspection of all the wiring from those two sensors to the PCM. Start by looking where the cable bundles come close to the engine or any other metal object to see if there is any place that the insulation is worn or frayed. Also look for signs of critters gnawing on wiring, etc.