2003 f250 sd (gas), 5.4, stock trans and rear end.

im 90% sure the gears went in my rear dif.(sounds like when your hubs dont disengage) plus the truck wasnt towing well at all today, i disconnected at the end of the day drove about 4 miles and the noise happened. if anyone has any other suggestions, that would be awesome. the noise is def coming from the rear end. if it is the gears is it difficult, any suggestions or tips? i have done a few on 94 f150's. thanks guys!