If the clutch still srips well you may want to consider our Firewall adjuster/quadrant kit, it allows you to adjust the clutch for proper actuation, and change the engagement point...
http://www.steeda.com/store/steeda-clutch-adjuster-kits-for-ford-mustang.html
What SoCal said, there is likely something blocking the seat track.
http://www.steeda.com/store/steeda-clutch-adjuster-kits-for-ford-mustang.html
What SoCal said, there is likely something blocking the seat track.