I had the problem. I changed the whole front end in one fell swoop. Both upper and lower ball joints, control arm bushes, inner and outer tie rods, and the sway bar end links. Then I only had to pay for an alignment once. The front end is set for a good long time now.

 

You might want to get the tires checked at a shop where they can check for damaged belts... my mechanic told me that he would occasionally see a tire that wouldn't balance up right no matter what they did, even with the Road Force system. Try rotating the front tires to the back to see if it helps.