Suspension Torsion Bar problems of the 2001 Jeep Wrangler

I purchased this vehicle new from a dealer. The vehicle has not been modified in any way. About 2005 it started to shake at highway speed. Did not know what it was and since the vehicle is driven mostly in town it was not noticed very much. Now that the vehicle is driven more it starts to shake uncontrollably at about 50 mph and then it will stop when slowed down to around 40 mph. I have taken it to 2 dealers, a mechanic and a tire store. Since starting to try to correct the problem I have had several repairs done. The tires were checked, the balance was checked, the alignment was checked, new tires were put on, shocks were replaced, brake rotors were replaced, torsion bar clips were replaced, and I do not remember the many other things that were replaced or repaired. The last dealer that it was taken to test drove the vehicle and said that he could feel the shake but he did not know what it was or how to fix it. He suggested that I take it to a frame shop. Since then I found out that other Wranglers have this problem and that it even has a name. They call it the "death wobble. " when this starts the vehicle shakes all over the and there is little control until you get the vehicle under 40.