Check rear axle torque and chain adjustment. Also check the rear wheel bearings. I had a wobble at about 45-60mph if I took my hands off the bars, checked everything including 2 sets of wheels/tires and constant balancing on different machines, turned out to be a faulty rear wheel bearing that was spinning on the axle. Put in two new sealed bearings(aftermarket) and polished the axle, all is perfect 15k miles later. Also check the steering head adjustment. More then likely its a tire or bearing problem.
I went through everything first too, did all new wheel bearings, new tires, had the balanced several times(dynamic, static, and bubble). had an alignment tool made for the swing arm to axle to make sure everything was aligned, even had the wheels an tires checked on a wheel truer and tried heavier oil in the dampner. It was driving me nut's.
Hopefully you can get lucky with new wheel bearings or something simple.
It' a bitch to change the stem bearings.