Thank you for the quick response. I think I am doing the right thing by exchanging it, however, I will say that it is a little daunting making sure the lens works as designed, because despite reading about the lens at length and following this thread, i found it a little difficult to trust my gut reaction, wich was to exchange it. In comparison, the 24-105 focuses very fast (and I understand that the range of focus is different for each lens), and so did my 15-85. The last straw was certainly the FTM not working consistently, that really baffled me and was the motivation I need to take it back.
In any event, thank you again, and I hope the new copy will work much better.
Good luck with the new copy, let us know how it is