Mine went at about 48K - came back with the Advance special ($150 - lifetime warranty). Same symptoms as above - Battery light and replacement solved it...
We have several PSD's and the alternator has been a frequent problem. Lately we have been getting rebuilt units from a local auto electric shop that our local NAPA uses. They increase the output of the standard 110A unit to 130A. Don't get one from your dealer, they all have the same problem built in.
Just be glad you don't have the "ambulance prep package"...I bought my truck used and didn't notice I had two alternators until both of them went bad in January...that second one is really tucked down in there!