Temp gauge jumps to hot
 

Greetings Ranger Nation,
While driving on the freeway and my rpms are more than 2500 for more than 10 minutes, my temp gauge will jump from in the middle (normal) to all the way pegged on hot in 1 second and stay there until I pull off to the shoulder. Then as soon as I come to a stop, the temp gauge will return just as quickly to the middle again. After that, when I get back on the road again, I need to keep the rpms below 2200 or it will keep repeating this pattern. I don't believe that the truck is actually running hot. Everything seems normal when I pop the hood. I have replaced the thermostat and coolant is flowing. Its a 2002 with a 2.3 and 5 speed. Around town and normal driving It runs perfect never any signs of overheating, Only when I am at prolonged times of over 65mph or 2500 rpms on the highway.