Tach function drops out intermittently Options

[digit3]

Hey folks,

Trying to figure out what I suspect is an electrical gremlin that causes my VDO tachometer to suddenly lose function.

I'll be driving along and seemingly out of nowhere I see the tach drop out. The needle bumps a tiny bit and my throttle sensitivity "dulls". I can feed it a little gas to keep the car running to get over to the side of the road while my alt light goes on and off.

Once to the side of the road, when I stop feeding it fuel, the car stalls. I can start it right back up and tach function is restored and I may have the rest of my drive back to normal.

My mechanic suspected an ignition switch which we changed out yet the problem remains.

I suspect that it could possibly be a bad ground?

Running a MSD box and 123 distributor on a 2.5SS motor.

Any idea on how to chase this down? I'm not super tech savvy and trying to avoid bringing it into the shop for every small detail however this issue is a PITA!

Thanks