There is a TSB for 2011-12 Challengers that have sunroofs and a sagging headliner (near edge of sun shade). The fix is the installation of two dual lock fasteners. They are attached with Duramix 4747 Super Fast Adhesive. Here is the TSB: http://www.wkjeeps.com/misc/Challenger/TSB/ChallengerTalk_dot_com/TSB_LC_2302812.pdf
I wonder why only 2011-12 Challengers? Mine a similar issue. When I have the sunroof open and go above 70mph the headliner droops. I just close the sunroof. I have some of that dual-lock at work. I should just do that
I work for Kaser as a mechanic and have had to use the Duramix 4747 Super Fast Adhesive for this headliner problem. Its not cheap but I highly recommend it for this sort of application. You don't want to messing with adhesive for this sort of repair.