1993 Toyota Pick Up Truck Overheating when over 60 MPH

I had the head gaskets replaced in May 2009 along with a New Radiator and Alternator. After 6 months I ahd to have the alternator replaced now when I drive over 60 MPH the Temperature Gauge starts going up. Then goes back down but after shutting off engine and restarting. Still I’ve owned the truck since 1993 and have never experienced this.

Did the problem start immediately after the alternator change?

On this truck, you have to drain the coolant to change the alternator (it really, really looks like you should be able to get the alternator around that radiator hose, but you can’t!). It could just be that the coolant didn’t get refilled properly and either the level is low or there’s air in the system.

Also, the usual (cheap) suspects: did the thermostat and radiator cap get changed at the same time as the radiator?

EDIT: Oh, head gasket(s)… I assumed this was a 4-cylinder. I’m not sure if the coolant would have been drained to do the alternator on a V6.

It could be a bad temp sensor too.

“Then goes back down but after shutting off engine and restarting.”

So the gauge stays up when you slow back down?

I also think it’s the gauge, or the line to the temp sender.
The line could be in the same harness as to the alternator, and was disturbed.