1999 Polaris Sportsman 335

Hi, my name is Jim and I bought my Polaris 335 Sportsman in 1999 new. I have had very little problems. It has a little over 2,000 miles on it. Last winter, when plowing snow, I noticed when I shift into reverse it would stall out intermittently. Last Saturday while on a ride in high range, it backfired and began to run like it does when in reverse without the override is engaged.

Does anyone have any suggestions as to what the problem could be? Any suggestions would be appreciated.

Jim