2005 Mazda Protege Flashing O/D light

evgod

ok so i've replaced the transmission. still flashes. i replaced the pcu became intermittent. i'm thinking now that it's a cooling problem. like the engine becomes hot on account of a leak at the water pump someone else seems to have installed incorrectly. i figure the transmission fluid gets hot at the radiator and puts the vehicle in limp mode. on a hot day the car is undriveable.
anyone got a clue? or want to tell me i'm right?