LO5 Jumpy tach, lack of power

On the way home from work the tach in my 92 RMW started twitching and jumping up by 300-500 rpm. The engine wasn't surging at all so it was just the gauge. There was a distinct change in the engine sound and a loss of power (needed to down shift to hold speed on the highway for even the slightest incline) and it will stall at idle. I went out after it had cooled a bit and it ran better (didn't stall) but the tach was still twitchy.
A quick search seems to indicate that it's the coil, but when I checked the resistances it seems to be in range. I'm contemplating replacing the coil anyway just because it's one of the things I intended on replacing in my quest to make this car as mechanically sound as possible.
Another item I heard could cause a problem are bad plug wires (my plug wires are new from when I bought the car, but they were a little short and so a couple of them are pressed up against the exhaust heat shield) but it seems to me that it should cause a misfire, not this, if a plug wire was to suddenly start shorting out.
Has anyone experienced anything similar?

My first impulse is the coil. The coil could be shorting to ground internally. You could check the ignition module in the distributor as well. Since you were going to swap out the coil anyway, take the leap, and if it does not fix it, then look elsewhere. You should swap out your wires just to make sure they are good.

When I took the air cleaner off to get access to the coil mounting bolt, I found that one of the fuel injector wire connectors was sitting up high and not clipped down in place. when i pushed it down the car ran great. So it was fuel starvation the whole time. I wonder why that affected the tach? The clip that holds it in place is busted so i'll have to order a new connector.