I've got a 65 st400 tranny that is having issues. I recently installed a 65 motor /tranny in my 63 lesabre. Once I got the motor started i filled the tranny with fluid. The tranny went into all gears but once it warmed up, It would not operate. I checked the fluid level with the engine off and it reads a little over full, and with it running it drops down to the full mark, but then will go back up to the previous level. If i let the car set over night and trany again it will start working again until it warms up. Could this be a faulty pump? seal? valve body?