Bad Drive Line Vibration

There can be side to side which can make other problems, and most mopars have that issue with the motor shifted to the side more.

Try the shaft angle and adjust the pin to meet that angle underload if the shaft is still doing it.
The shop you left sounds as if they have a different machine and it spinning at 3500 is faster than most other machines.
since they found no bends i wonder if that was it, which weight did they add, was it like 1/16 or 1/8 thick ? and 1", 1.5" or 1.75" across ?