I recommend having an engineer that specializes in cracked slabs do a report on it as it will eventually be needed; I have used SD Engineering 760-632-5474. For repair of the slab I have worked with Craftsman Foundation Repair and RAD Construction.
I would suggest contacting Russ Burdeno of RAD Construction (website attached.) I have used him a number of times in our real estate transactions, and found him to be very knowledgeable and honest. Jeri Hess, Century 21 Award