I have a 1991 Mustang GT with AOD Transmission and 3.73 rearend gear (with correct speedometer gear also). When the car is cold it shifts first through overdrive perfectly. When the car is warmed up it shifts great first through drive but to get in overdrive you must let off the gas completely and it goes in overdrive around 40 to 45 mph. Fluid looks clean no burnt smell, also no slipage in any gear. Ive adjusted the Tv cable, set at just a hair over mid like it said in forums. Thought I might try a external transmission cooler since the differance was after the engine was warm. Maybe flush transmission fluid and change filter and fluid. I've always had 5 speed cars so this automatic stuff is new to me any help would be great.