2002 2500HD 8.1l Allison Trans. In 4wd only, it feels like one side or the other of the front axel is wanting to spin slower than the other. On dry pavement,(yes, I know, don't use 4wd on dry pavement but I just did this to get a feel for what's going on) I can actually hear the tire dragging on the pavement during acceleration. When not accelerating, it is fine. On snow it pulls the truck to one side or the other, then releases sending the truck unexpectedly in the other direction. After this started, I checked the fluid level and it was pretty low. I topped off with 75w90, per the manual. No friction modifier. Would synthetic be better? The truck sits a lot and I thought maybe the clutch pack had siezed up, although I'm not sure it has one. Thanks in advance for the help and for the forum. Tim After some more thought, it could also be that one wheel is locked, as it should be and is actually being pushed by the rear wheels because the front propellor shaft is wanting to turn slower than the rear. I don't know what could cause this either though. Anyone have any ideas? Also, why is there an actuator in the front diff? To lock it in 4wd? Doesn't the transfer case handle that?