1999 Chevy Tahoe Voltmeter spikes to 19 Volts

My 99 jeep did the same.
Jumped to 19 volts on guage then down to normal when slowed down.

I had the aternator taken apart and the brushes and commutator were worn badly after 190,000 miles.

So my guess is at high speed the wear was evident and caused the computer to say 19 volts as a warning.

Simply replace the alternator or have rebuilt like I did for $60. Better replace starter too as it must be worn also.

Sometimes it can take 5 days or so to get a alternator and they can be hundreds of dollars of $125
better get too it as the 19 was a warning it is worn out.