I say his is not tuned correct or not driven correct. 1991 is 0 to 6.6 sec and 1999 it 0 to 60 7.5 . My source is here.
http://home.pon.net/hunnicutt/SHOpage.htm Was considering a v-6 sho in a mustang. It can be converted to rwd. Ps the fastest one is a v-6.