James, read my post here:
I had the shakes at about the same speed as you. Not full-on DW all the time, most often just the steering wheel shakes, clearly a precursor to DW. I did get DW a few times. The shakes and DW were more noticeable when I would rotate tires.
I read hundreds of posts, and paid careful attention to those who knew what they were talking about. I checked my bearings, TREs, track bar/mounts, tire balance, ball joints, all seemed to be OK.
I decided to attack my problem by replacing the front lower control arms. I understood that the factory LCA are marginal at best when new, and I had placed a strain on them with a 3" lift for the last 30K miles. It made sense to me to buy LCAs that would adjust, compensating for the change caused by the lift, yet provide a solid, positive tie-in to the frame.
When I removed my factory LCAs, I slipped the stock bolt back through the sleeve, and I was surprised at the amount of slop between the bolt and the sleeve... yet the sleeve showed little wear or distortion. I could visualize that amount of movement... in each of the four bolts/bushings... and could easily understand the shakes and DW.
If you check all of your other basic steering components and find them all good, you should consider going for the Currie or Savvy JJ control arms...
it worked for my rig.