I too would be suspect of the cable. Since things contract when cold, the cable may be just a bit too short. I would have to look at mine (which is not near me) to figure out if it would be in both directions or only one. There should be an adjustment on the cable.
Also of note, I have the ZF tranny book for mine. I dont think that yours is the same tranny as mine (45c or 63c), but I believe that you do have a ZF. If you find out is it, I can Email it to you. I down loaded the manual from either ZF direct or from skiDIM. skiDIM has lots of manuals you can down load. Just go to their site and shop for manuals. Maybe the manual will help you out?
1996 Prostar 205 LT-1