Our 2013 Bus has a Powerglide chassis and we've been running it for over 110,000 miles. Nothing to be concerned about. All Tiffin did is use all sorts of commercial, commonly available parts and bolt them to their frame design/assembly. Bendex brakes? Cummins engine? Allison trans? xxx front end? and so forth. Any shop that deals with heavy trucks, RV's or general repairs should be able to work on your rig. Yes, the number and location of the grease zirks will be different from what they're used to, but a good shop will cope easily. We've been extremely happy with the Powerglide, and as you can see we don't let too much grass grow under it. I do all my own maintenance with locally available parts.
2013 Tiffin Allegro Bus 43QGP
2011 Chevy Silverado 1500 Toad