That solution has crossed my mind.

I replaced both motor mounts with old used ones. One has a MOPAR number the other is an old aftermarket I believe. The rubber in them seemed much more pliable than the rubber in the new mounts. Anyway, no change in vibration. I removed the transmission mount to take another very close look at it. It looks like what it is, a brand new rubber mount. When I bought the mount, the metal U-shaped bracket that holds the insert was made from much thinner metal and looked flimsy. I removed the rubber insert with its steel shell and installed it in my original bracket. The original mount rubber was junk. So, I don't have an original trans mount to try.

I ran the engine with the trans mount removed, and the vibration was pretty much gone. Possibly completely gone. I had the car in the air on my lift with the trans supported on an under lift stand, so I had to use a ladder to get in the car and start it. I did not run it very long since my garage door was closed. I also did not get under the car while it was running to see if I could see/feel any vibration in the transmission. I may repeat this test with some additional help, but not sure what more I could learn from that. I think I've learned that the vibration is being transmitted from the engine/trans through the trans mount into the body. I suspected that was the case, since I could feel the vibration in the seat and steering wheel ( and see it in the steering wheel) but could not feel it anywhere under the hood.

I'm thinking I'll pull the valve covers first and do some inspecting of the valve train to make sure all is well there. Then maybe the intake and valley pan to get a good look at the cam and lifters. Could a bad lifter, bent push rod, bad rocker, or even a cam that is going south on a cylinder cause an imbalance in the engine firing that transmits through the mounts to the body? It is a stock flat tappet hydraulic cam with the original pushrods and rockers.

R/ John