Anyone running an aftermarket coil in a 22RE?

I've installed one in my junk, after I discovered that my timing light wasn't firing as consistently as it should. I replaced the cap/rotor/wires and went ahead and got a hotter coil (slightly larger).

My issues is that when the key is in the ON position, the tach wanders a bit.. It'll continue to wander once the car is running, which makes the tach about worthless.

I realize that the tach is driven by a voltage feed off the ignitor, but I'm wondering if anyone else has seen or solved this issue?