My first thought on this was axles and/or the torque converter lockup. Both can cause this issue. Plymouth has a ton of TSB's out for this issue (example: 18-05-94 SHUDDER DURING TORQUE CONV EMCC OPERATION -41TE/42LE). Worn out axle ends will cause this as well. Apparently the remanufactured axles don't get new inner tripods, making the issue continue even after replacement.
This is a bit of an odd forum to post this question in. Do you have access to IATN ($15/month) or Identifix ($130/month)? Both of these services are absolute lifesavers. IATN is a forum tool for asking those really complex questions. Identifix is a massive database of searchable fixes with numerical likelihoods that your issue will be solved by a certain fix. They are worth every penny.
