Plymouth Repair: Chrysler Plymouth Transmission, washboard road, chrysler plymouth

Question
I have a 1996 Plymouth 3.3L with  automatic transmission. When traveling between 60-80km p/h (35-50m p/h), and accelerating (or travelling up hill) the vehicle will begin to shudder (like driving on a washboard road). To make it stop I simply temporarily stop accelerating (a second or two) and then re-apply the gas to continue accelerating, and the problem disappears. It doesn't happen all the time and I can't appear to do anything to make it happen. When it is happening if I leave my foot on the accelerator it will continue to shudder until I ease off. Fluids have been replaced. I've had the leads replaced thinking it might be an intermitant lead affecting the engine distribution but that hasn't resolved it. Could it be a synchro between third and fourth gear? It has never happened while decelerating or outside those previously mentioned speeds. It's been to a few different mechanics over the last 8 months (since it started) but not much help and I'm cautious to spend much money "researching" on such an old vehicle. If it is in the transmission, how scary might the bill be?

Answer
The washboard shake you feel is the torque converter slipping. The only fix is to have it replaced. However concidering the age of your vehicle, the transmission should be rebuilt or replaced at the same time. I cannot speak how scary the bill would be. Prices vary greatly from shop to shop as well as regions and it all depends on what needs to be replaced. A very rough estimate for a total replacement/ rebuild could be around $2000.00.