I had the BCM flash done at the dealer a week ago. The DRLs dim when the headlights are on. I did not notice my DRLs staying bright with the headlights on before the update. My guess is it's a software glitch and sometimes they dim and other times they don't. The software update takes care of that glitch.
The change I and others on the forum noticed after the update is that during the day if you turn your fog lights (Yukon only) on, the DRLs will stay bright. Before the update the DRLs would dim if you turned on the fog lights.