Dave -- Assuming it actually had a locking Dif. (not limited slip) did they instruct you on how to lock and unlock it? As I understand it, you only lock difs. for a short period of time when stuck or towing in a straight line up a steep incline. They are left unlocked most of the time because otherwise the wheels will chirp and bounce in turns on the road because in a turn the outside wheel travels at a faster speed than the inside wheel. I have seen trucks with locked difs. do this around corners. I understand some systems, like on the newer Jeep Rubicons have a pulse system/button for quickly locking and unlocking the difs. so you can both power through the mud and turn. Never had fully locking difs. so this is only my understanding of how it works; I could be wrong.