Charging problems

[37Driver]

Early 1999 F350 4x4. A few months ago after sitting overnight the truck wouldn't start due to low batteries. After a jump start it didn't occur again until two mornings ago. I assumed I had a battery problem. I drove the truck from North Carolina to Indiana without shutting it off. It started normally the next morning and I made the return trip home. It fired right up this morning and made a one hour trip, starting up several times with no problems. While returning home I noticed that the EGT gauge was pegged, shortly after that my GPS which was plugged into the power outlet started flickering. I pulled into a drive thru a few miles from home and tried to lower my power window. it stopped and started several times and finally stopped. The radio, GPS and vent fan also shut down and the airbag light was on. The volt indicator was showing below the normal charge line. I started for the house wondering if I would make it, then the volt indicator slowly rose up to a normal level. The airbag light stayed on until I shut the truck down. It restarted normally and the airbag light went out.

Anyone have a theory here? Alternator or something worse?

Thanks