Do a search here and on DTR under belts - many of us have had this problem, ALTHOUGH, most of us with new belts (my original went at 5400 miles) have had no additional issues (knock woodd). I have about 14,000 miles on the replacement - so far, so good. Like you, my dealer found no alignment issues, but I have been paranoid ever since.
There is apparently a fix for this now, which involves relacing the alternator pulley with an "overrun" pulley. This will help eliminate the "chirp" on shutdown, which is common to ALL diesels, BUT puts a strain on the belt.
It is VERY easy to install these incorrectly. There is no room for error on a couple of the pullies as well.
Do a search on posts for "Sag2" here, and you should find his thread. Hope this helps.