I finally got my 86 2M6 out on an extended freeway cruise. When I engage the cruise control it works, however, if the speedometer is registering 100 km/hr. when I engage the cruise it immediately accelerates to 108 and holds that speed. The tap-up and tap-down features both work as expected. Is there an adjustment that can be made to correct this speed increase problem?

I'm not completely sure but I'll throw out an answer anyways, maybe move the cable on the diaphragm one pin further out so the cable is a tad bid looser. Not sure if the computer with overcompensate and do the same thing or not but that is what I would try first.