+1 it seems very odd that it would do thatCheck down by your pedal and see if the carpets not rubbing it or catching.
ReallyIt's been the subject of recalls:-
http://consumerguideauto.howstuffworks.com/1994-to-2004-ford-mustang-9.htm
LolsIts alive!
+1 carpet happened to mine, I had to shave an inch or so off near the pedals, the clutch was catching as well at timeHi, i agree check the pedal and carpet and the throttle spring.