Tom has given you an excellent answer with many good ideas One thing he did fail to mention is the viscous coupler . You mentioned it was an AWD and one of the week points in the system is the carrier bearing in the back of the coupler .This is a inexpensive bearing but you will need someone to take the coupler apart to replace it as the dealer and most shops will want to replace the whole unite which is extremely expensive. The viscous coupler can be replaced in under an hour but the unit can run close to $2000 . If you can find someone to replace the bearing there will be another hour of labor but the bearing will probably only be 30-40 bucks. Just something to look at . Hope this helps