Mad Dart,
I just went through this with my duster. I even started a thread to ID the shifter I had. I eventually went with the set up from Brewers. They were very knowledgable and a big help, they are more expensive but not by much so its worth the extra expense to get the exactly right parts. In the past I have had trouble like what your experiencing. I am assuming that your have a hurst shifter not an inland. One thing I have always run into with old shifters is rough gate to gate shifting like your talking about. I went and spray some wd-40 down into the slide plates since they tend to bind when ever you disturb the shifter. If it makes it better then take it apart and clean and grease the slides. I hope this helps.
