I have a dana 80 in my Ford chassis motorhome. I think it has 5.23 gears. I towed a 24' enclosed trailer to the desert several times a year full of desert toys. I have about 25,000 miles on it. It specs. and I use 75-140 synthetic oil. An axle seal is leaking for the second time now, first one replaced under warrantee (both replaced). I noticed recently that the differential housing changed color, it actually looks burned like it seriously overheated. I checked the synthetic fluid and it looks like new.