Please note, this vibration started after about 4 years on my old set of tires. Those were Goodyear tires. What I'm trying to say is that for about 4 years, on the Goodyears, I had no vibration issues, I get in one day and all of a sudden I have a new vibration. It was not bad to begin with but got worse. The Goodyear tires still had good tread but had started to crack between the treads all around the tire......they aged out before wearing out. Those old Goodyears had about 55 thousand miles on em so I felt I got my monies worth. I had a set of Cooper tires installed about 6 months ago but the vibration persisted. Tires were balanced when purchased and my mechanic said he took them down to the local tire shop just to double check the balance job and they all checked out OK.
Mechanic says front disk rotors, brake pads and wheel bearings are all OK. I had him install some new Bilstein shocks but problem still persists after that, no change.
With all that said, that is one reason I thought maybe a bad u-joint as I had a similar issue many years ago with another vehicle.
My next guess is the harmonic balancer. I think vibration is in the driveline and torque converter problems are usually "noise" problems not vibration.
Take care....John