Just adding in to what the others have said; The problem is most likely the regulator and there are a variety of fixes.
My most recent fix was on a '97. I was going to do the 'bicycle cable' repair, but noticed that there was an adjustment built in to the particular regulator I had. A few turns on the adjuster and it was fixed.
On an '01 I replaced the regulator and the problem was still there. I checked the motor and it had a lot of play (wear) when reversing directions. Replaced it and it has been good since.
The
tech article that Rex linked is a great step-by-step as are most of the
Pelican Parts DIY articles.