2001 Mazda Tribute Transmission problem P0732

The other day I was driving my Mazda tribute, I went to overtake a car and the car kicked down to first gear (when it normally only drops to second) and the vehicle seemed over responsive. The next day the OD light began flashing and the car would not change gear from a standing start until the engine was revved to 4500rpm. The auto seems to shift harshly and occasionally shift very firmly and thump the driveline. The oil does not seem discoloured or burnt. I Changed the transmission speed sensor due to a P0723 code appearing on a hand scanner but this did not fix it. I took it to a repairer and got it scanned and it came up with P0732. Due to the initial over revving I feel that the problem is electrical and possibly linked to throttle input, but I'm not sure. Can you shed any light on this because this has me well and truly baffled. I eagerly await your opinion
With thanks - Simon