I've got a 2011 V6 mustang manual that occasionally shudders when I engage the clutch in first gear. It's intermittent and I have been able to track down the issue yet. The car has 60K miles on it and is mostly stock. No mods to the transmission.
I heard about the ACT flywheels, they sound like a great way to get rid of the stupid dual mass. Did it get rid of that driveline vibration between 2500 and 3000 rpm that the DM flywheels seem to have? Any difference in overall driveline vibration? Lastly, how many miles on yours when the clutch started to fail?