Just installing a shift kit wasn't good enough; we needed a throttle valve cable so our right foot could talk to our transmission. Now the trans works like it's supposed to: Downshifting when we romp on it, holding the gear a bit when we lift, and snapping off fast shifts when we stay in it. This was simpler than installing a manual box, and we're happy with its performance so far.
http://grassrootsmotorsports.com/project-cars/1986-98-mark-vii/getting-most-out-shift-kit/
