Ongoing vibration issue

Haven't chimed in in awhile, but looking for more opinions on an ongoing vibration issue I have been dealing with in my Duster that nothing I have done has alleviated the problem. I have a noticeable vibration that starts around 2200 rpm and gets very noticeable at 3000 while the car is at rest. It becomes less noticeable above 3200. Makes the car unenjoyable to drive since that rpm is right at cruising speed between 55 and 65, and begins to pulsate at sustained speeds. Again, this occurs while the car is standing still. I started by changing everything external like torque converter, flexplate, harmonic balancer, unhooking accessories, with no improvement. Finally decided to build a new motor thinking it had to be an internal issue in the engine. Built a 408 stroker and still have the same results. Though previously everyone said it couldn't be the transmission, I have to wonder since it is the only thing left. I did convert my engine and tranni mounts to urethane, but would be surprised if that could be the problem. The tranni is a 727. Wish I could run the engine with the tranni unhooked, but not on a MOPAR. Anyone ever had an issue with the input shaft or pump causing vibration issues? Thinking of trying to find another 727 that I can just throw in there for testing purposes. I am out of possible causes, and the solutions so far have added up to quite an expense. I must say though that the 408 is very welcome under the hood over the 340.