The 6 speed was based on the 4 speed electronic transmission. As far as electronic transmissions go, it among the best, certainly not as troublesome as those with more speeds. It's reputation is pretty good. You only hear about the bad ones. There's lots of good ones out there. Just ask LEVY. He doesn't even have the fluid and filter changed and his two 62TE transmissions perform flawlessly (unless they collide with a rock )The trans guy didn't say anything, just says the way they are built isn't the greatest. My regular mechanic doesn't do trans work, he isn't a fan of Chrysler.
At this point, the trans guy is suggesting dropping the pan to see what's there and then going from there. Debating whether to proceed. Do you think that would help assess?
Yes, drop the pan to see what's going on there, if anything. A clogged filter could mean the transmission is grenading. There's no other reason for the filter to be dirty. There's no air dust or combustion byproducts in a transmission. Then again, the filter is there to protect the transmission from whatever. Perhaps something wrong with the filter itself, a bad product. Has he fluid ever been changed? by a reputable Shop?
Then you have to be prepared for "what's next?'. A Jasper rebuilt transmission, or sorting out the electrical. Your transmission guy seems to be offering the correct approach.