Front end vibrations

I have a 2001 ford f-350, 310,000 miles, all original.I recently had a lot of front end work done, brakes, rotors, shocks, tires, alignment, etc. I noticed at 7500 miles my tires were worn out on the inside tread and the out sides seemed new. I took it back they replaced tires, they said they were bad tires, rechecked ailmingment and sade everything was fine. The problem is a moderate to severe, shake or shimmy when I travel at higher speeds. 60mph. Fine, 65 mph. Little shimmmy, 70 mph. Shaking and troublesome. Any ides on what to check next? The work was done at a ruputable ford dealership that I have been using since '95. Thanks