My 2000 GP acted the same way most of its life. I didn't worry about it because my commute was 50 miles of freeway and rarely stuck in traffic. Late in its life the radiator side tank was leaking so I put a new radiator in with new upper and lower hose and a thermostat. After that it held a solid temp so it was one of the 3 things that fixed it. Guess is radiator flowed better.
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