I JUST BOUGT A 13 XM 163,IT HAS ABOUT 300 MILES ON IT I NOTICED THE REAR SKID SAGS A LOT .YOU CAN LIFT UP ON THE REAR BUMPER THEN LET GO AND THE SLED WILL SAG ABOUT 6-8 INCHES.IS ONE OF THE REAR SHOCKS BAD?THE IS NO SNOW ON THE TUNNEL,THE SLED IS TOTALLY CLEAN OF SNOW SITTING IN MY GARAGE,NOTHING ON REAR OF TUNNEL....I WEIGHT 220 LBS.ANY THOUGHT ON THIS........