The 99 Big Bear 350 has the adjustable shifter linkage on the left side of the engine, down right by the shifter. You'll see it moving up and down when moving the shifter. Adjust this rod to see if it improves the issue. Additionally, if the rod ends are worn then this can cause issues as well.
Normally this rod only changes the height of the shifter, but it might cause your issue. It's worth a try.