Does the level of DLC missions adjust to my current level?
Solution 1:
Once you take a mission the level for that mission is set in stone. However all missions after that mission and missions you haven't taken yet will continue to scale as high as they're set to scale. See this answer for DLC level ranges in playthrough 1; most max around 30. In playthrough 2 the DLCs will max at 50, which is also your max level. Since you're already at the end of the main storyline you'll probably just want to start playthrough 2 before doing the DLCs.