In digging thru my manuals, Spartan makes mention of a two speed rear axle. I have never heard of one being used in a motor home or bus of any kind. So does anyone know if it really exists.

Yes Gary, Santa 2 speed axles do exist. I have regrettably seen and worked on many.

In my line of work the 2 speed axles are considered weak and problematic. Shifting should be done in the transmission. Overdrives, creeper gears, lower/higher shift points are all obtainable in the transmission. I feel that there are no real benefits to a shifted rear axle on a big truck.

I have not seen a 2 speed rear on a motorhome. I am sure there are probably some, never having seen one in an RV, I can't say for sure.