Truck shut off while driving?

[Mattys1970C-10]

For about two weeks, right when I start the truck it would squeal like crazy like a belt sound, and then id turn the truck off, start it back up and it was fine. this happened once or twice a week maybe, just squealing and then id restart it, and the noise would be gone. today i was driving it, made a stop, turned it back on and couldnt get the squeal to stop this time for about ten minutes. finally stopped, drove it again and stopped for food, now it wouldnt even crank over, jump started easily, and ran fine but there was a slight high pitch tune under the hood that went up and down with rpm, then about 20 minutes later the whole truck shut off, no radio, no juice, nothin......what happened? is this an alternator?