Hey guys

Wondering if you could help me out with a problem I recently have been experiencing on my 05 4.8is

At any speeds of 70km/hr or above, the steering wheel starts to shake excessively. I retorqued all of the wheel bolts but that wasn't the problem. A few weeks ago, I got a new tire rod and alignment done at the local dealership (alignment done since I got 20mm spacers on the back).

Any ideas as to what might be causing this problem? I've been back and forth to the dealership multiple times in the last few months with problems

Thanks!!