I'll take a stab, my drum will cook faster so i adjust and not stick to a 3-2-1 or 2-2-1 i go by it being done (bend test or tooth pick comes out clean)
Do you use a deflector in your drum? I have done ribs not using mine and found it got done faster.
Long story short i think you over cooked them if they looked done and the passed the donenes test they are done regardless of time.
A bunch of Webers, a UDS and a Happy Cooker!