KCG, pretty much the same deal happened with me too. Mine was performed in Sept. of '14. The "bulletin" was issued (I'm guessing) a month maybe before that. At first is was going to be an update, then it turned into a radio module replacement, and update. They had to order my radio also. I'm assuming they don't keep those modules on the shelf. My truck was built in 10/13. I got my truck 2/22/14. Like I posted, I do not remember the build cutoff date for the software only update, but it's obviously after 10/13. I'm not sure what this deal falls under, as it's not a recall, but somehow it's still like warranty work. Possibly why you didn't pay anything.
My radio was a lot better after the change, but it still has it's problems. Certain stations continue to drive me nuts. One in particular that I listen to that broadcasts the Pirate baseball games, still "repeats" play by play like a skipping record. Unbelievably frustrating as these trucks are going on 4 years old now, and this radio deal, unfortunately, is what it is. Chalk it up to "minor league" engineering by GM. If I had any say about it, those involved couldn't have been fired fast enough.