I have a '72 142E with a BW35. In second gear between 25mph and 35mph and in third gear between 50mph and 60mph the car shudders hard. This shaking is even more pronounced under hard acceleration. However outside those speeds the car does not shudder. This problem has continued in spite of replacing the ATF. Because the car runs smooth and the problem is not felt outside those speeds I believe that the problem is the transmission, is this a safe assumption? Given the symptoms should I replace the transmission or just the torque converter? Any help would be greatly appreciated.

Thank you,
Colin Spikes