My 2001 pathfinder LE has over 130k and now the engine is overheating.

I have replace thermostat but the engine stil overheating when is running on highway. Once i slow down to about 60 mph it drop down close to normal temperature.

Any suggestion on what else i should do.

I thought about changing water pump but the cover was seal too tight. Any suggestion on how to break it off?

Thanks in advance.

Check your radiator for dirt/clogs.