12-A not Revving Properly - "Stuck" throttle
 

I have a 85 12-A. It is slow to reach red-line (most of the time). I thought it was a clogged cat, BUT - sometimes it howls right up to the redline and beyond... This is always accompanied by a stuck throttle - i usually up-shift, where it settles about 4000 RPM and eventually calms down, usually running very rough as the RPMs come down (eventually). Any ideas?