My 98 has the same problem. Pull the door pannel off and watch the bottom of the glass when you raise the window. Mine had become loose in the bracket allowing the rear od the glass to pull up out of the bracket causing it to bind.
Next time you roll the window up, try pushing down or pulling up on the rear edge of the glass and see if it speeds up. If it does, all you need to do is clean the tracks and tighten the bracket that holds the bottom of the glass.
Zig