I have a 99 Durango with 63K miles on it. When I'm driving above 35-40mph with slight acceleration the transmission tries to downshift and then it immediately is back to normal (the engine briefly surges...RPM's jump up then right back down). It happens very quickly but fairly regularly. If I lightly tap the brake when still accelerating I can make it happen routinely. I've been told it's a bad torque converter and that I would be wise to rebuild the tranny. Hoping it might be a simpler problem i.e. Transmission output speed sensor etc.

Ideas or suggestions please!

 

May want to replace the Throttle Position sensor. Engine RPM surges can by caused by this faulty sensor.