[5thwheeler]

We just changed both front & rear ends, transmission (NV5600 6spd.), transfer case and crankcase fluids replacing them all with Amsoil.
As bad as we are at remembering when to change the fluids we figured we may as well switch to the leading synthetic on the market and eliminate any possibilities of damage caused by a fluid with too many miles.
It was kind of expensive to do but when you take into account the longer drain intervals its actually cheaper. They claim dramatic mileage improvments but I remain somewhat shy - time will tell.