Drove my 1988 Suburban with 700r4 about 15 miles, stopped and did some shopping. Half hour later started up and no reverse at all, seems to be slipping in drive also. Stopped by shop on way home and they said that drive will go out soon. 2500.00 rebuild is what they say. Anybody have any opinions as to what is actually wrong, and if there is anything I can check myself before going back to shops for quotes ???