I think I cured this issue. I drilled three 3/16" holes around the perimeter of the thermostat. After I fired it up, the temp slowly rose to about 170-180 and stayed put. I think the thermostat was definitely warming up too slow, and by the time it opened the internal water temp inside the block was too high. The three small holes allowed a small amount of water to circulate, keep all the water at a more even temp while warming up, and most importantly brought heat to the thermostat so it could be more in tune with what was going on temp-wise deeper inside the engine. Thanks for all the input guys!
