So I confirmed that the thermostat was replaced.
Now that the weather is getting cool I haven't had any issues with the car over heating for about 3 weeks.
Also now that it is getting cool I have no heat for the interior of the car.
The two possible causes I have come up with are:
1) A clog causing reduced flow which is more noticeable at high RPMs when the higher flow rate is restricted
2) A mechanical failure of the pump causing reduced flow at higher RPMs
What is the best way to clear or find a clog?