I had the same experience as Pamlico see my previous post awhile ago. The reason for this is that they forgot to request that you rotate the tires at 5k intervals in the book and in the automatic reminder maintenance notification system. Initially the 04 XLR's were to get wider tires in the rear and the books were printed with that in mind (no rotation fornt to rear).
Remember that the non-V's have the same size tires front and rear.
So GM was "on the hook" for the 1st set. There shold have been a form you signed acknowledging that you agree to rotate the tires from now on.