Danny, while a hint of blue smoke may not be normal, it certainly isn't unusual for a 2 cycle detroit. I'm guessing your bus has a 6V92 or maybe 8V92. Both are 2 cycle and will burn a little oil on start up after they have 50,000 or more miles. Now the going up hill stuff is a little different. I'm not a mechanic, but I have stayed at a Holiday Inn.
I talked with a Detroit mechanic yesterday who said the book on the 2 cycles says do an inframe at 250K and a total overhaul at 500K. That was sooner than I thought! I got spoiled when I was driving someone else's Series 60. Can't afford one of those for myself, yet!
Do you know the history of your bus engine? Or even just your bus? May help you to guess the miles on the motor. Darren