305 TPI. My temp gauge is always reading high. I don't even have to start the car and it'll go up slowly with the key turned. I disconnected the connector for the switch near the 1 and 3 plug and the needle went down to 100. New gauge and new switch.

 

Replace you temp sensor. It likely crapped out with old buildup.

Then...flush your coolant system, refill with 50/50 mix, make sure there are no leaks. That's a good start.