I just began (in the last month, I have a six-month-old 2007 X5 4.8) to see the acceleration decline in 2nd gear (automatic mode). Off the line, I still get tremendous acceleration, but in 2nd the acceleration declines so much I can redline the car (in automatic, mind you) before it finally picks up (around 40-55 mph is when it picks back up). Steptronic shifting does not reduce the decline in acceleration.
Not sure what the problem is, but am taking the car into the SA dealership (been told there is a one-month appointment wait-list, believe it or not). The car drives okay, I just have no power. That's not what I paid for, I guarantee you. A car this heavy, in which you have become used to the acceleration, is dangerous on the road when all of the sudden it stops working the way it has for six months.
I am going to give the 2nd FOB a shot tomorrow, and will report back.