After about 10 minutes, guages Move wildly and engine stalls

Engine: 4.3L V6

After driving (or idling in the driveway) for about 10 minutes the tachometer and battery gauge will bounce wildly from side to side and the engine will stall. It won't immediately start back up, but if left to sit for awhile it can be re-started.

History:
The fuel pump has been replaced twice, most recently about 2 years ago. Both times the fuel pump has gone bad the symptom has been a no-start (at least without the aid of starting fluid) but it never stalled.

The gauges (all of them in the cluster) have worked when they felt like it and been dead when they didn't for as long as I've owned it (about 5 years.) This issue seems more prevalent in hot weather or after the heat has been on awhile in cold weather.

I recently replaced the serpentine belt, alternator and water pump to try to eliminate a "belt noise" kind of sound.

I've replaced the battery with no change in symptoms.

I'm getting no error codes.

Probably just a coincidence, but I have quite a coolant leak - still trying to narrow it down, but I fear it's the head gasket.

With the gauges doing a dance, it makes me think electrical. Any ideas?