how much will it cost to repair rear differentail, can it be fix, is a new one needed

Your description sounds like two separate issues, one being the differential and the second the Transmission. An overhaul is generally what is needed. New bearings and in some cases a new gear set.My recommendation is to take your vehicle to your local dealership for inspection and diagnosis. A differential (Rear end) rarely needs replacement. They have the special tools required to perform the differential overhaul in a timely manner and diagnosis your transmission as well. .

See Johnny's answer