After a complete rebuild job on the automatic transmission it has lost all main line pressure in just 300 miles of driving. The pump pressure regulator valve was not stuck. After draining the ATF I found it to be milky pink and the fluid level was much too high on the dipstick. Draining the coolant showed pink transmission fluid floating on top. From what I can tell the only way the two could get mixed is because of a leak in the radiator/transmission cooler. Any other ideas?