99 Monte misfire, (& Scanner Recommendation)

I've got a 99 Monte with a 3100 engine.

Rarely, the engine starts misfiring on a tip-in.

When this happens:

1) The engine is greatly reduced, (occasionally stalling) 2) The tach jumps about quite heartily 3) The "VOLT" light flashes as the engine nearly stalls 4) There is noticeable backfiring out the tailpipe.

This may happen for a few minutes, then disappear for weeks.

Not specific to rain, cold, road surface (bumps).

I've been trying to determine the source:

1) Looked for loose wires 2) Unplugged MAF, no change 3) Replugged MAF, unplugged MAP, no change 4) Throttle is next. (Looking for intermittent sensor)

I wonder if the crank sensor is loosing synch. This is hard to unplug for obvious reasons. ;-)

Any ideas?

Also, I'm figuring I'm going to need a scanner to obtain additional data. Any recommendations? I'd like the scanner to be usable on more than just my GM car. Perhaps CLASSII and CAN?

TIA