Was riding around in 2 wheel drive on creek and went up a couple small hills and leveled off. All of a sudden differential light starts flashing and emblem on the screen was flashing too and engine started sputtering. Had to put in 4 Wheel drive and lock in differential before I could go without engine sputter. Shut it off later and restarted and drove in 2 wheel for a bit and started up slight incline and it started doing the same thing as before. Any ideas on fixing this problem. A little tiring having to drive around with differential locked in.