Both the 41TE and 62TE are full electronic transmissions.

The solenoid pack controls the hydraulics within the trans.

Driving in 3 (if a 41TE) takes you out of overdrive, raises engine speed. But you still have lockup.

Lots of things can cause harmonics like you are going through. Could be converter, engine firing instability but not bad enough to cause misfire.

I would burn the tank of fuel you have and fill it up with 93 and drive it like you stole it for a bit. I’ve seen many cars clean themselves up this way. If that doesn’t fix it yiu’ll Have to dig deeper. Wouldn’t be a bad idea to start with plugs.