I have had enough with the same issue and the dealer keeps on telling me it's always something else.

I have a 2006 x5 4.8is with 39k miles. Between 60-75mph the whole seat and gas pedal vibrate. The steering wheel does not vibrate at all. First they told me it was my tires. I bought all 4 tires, then it was my wheels. I requested to try different wheels and the problem persisted with the other set of wheels. Another issue was alignment. I paid for an alignment and the problem is still there. I have two other BMW's and have had BMW's for the last 12 years. This is very frustrating and I am receiving no help. What do you guys suggest I do?