I would check to see if your water pump is working correctly. If it's only putting out like 50% of the pressure that it should...(easy to check as well, IME)
X2 Seen many a motor with the impeller fins on the water pump eroded away due to either never having a cooling system flush/coolant change or insufficient grounding present these symptoms. If you pull the WP and the impeller is eroded away make sure you have good ground straps, otherwise the coolant is the ground conductor.
1stgenboy
