I recently got a 99 crv which keeps starting to overheat when I've driven for about 15minutes at 60+mph. After that time if I'm over 60 the temp gauge starts to climb to red. I've never let it hit red but it gets close. If I back off the gas it will go down immediately.

ive done a full flush of the radiator, I bled the system for air and had a mechanic check for leaks. The ac and heat both work.

My next step was going to be replace the thermostat. Anyone have any other suggestions?