GM Guy
Manual Trans. 2WD Enthusiast
Nice find! On your tach not matching the supposed ratio, double check the glovebox codes to see if axle tag and original build match, and if so, check alternator pulley. if it has gasser pulley, that could be why its off.
On the diff oil, 80w90 is supposedly 3,000 mile change intervals, 75w140 syn. is 30K intervals, as theDana 80 is hard on oil. The NV4500s seem to not mind the Amsoil NV4500 approved oil, unless its super crisp and deserves the GM stuff, mine get Amsoil. if its not directly approved for it, dont run it.
On the diff oil, 80w90 is supposedly 3,000 mile change intervals, 75w140 syn. is 30K intervals, as theDana 80 is hard on oil. The NV4500s seem to not mind the Amsoil NV4500 approved oil, unless its super crisp and deserves the GM stuff, mine get Amsoil. if its not directly approved for it, dont run it.