3406 Cat. that would be an E engine. Joe is correct. Best engine Cat made; we have two of them. From the factory they are rated at 475 HP but you can safely have the injector codes changed to 550 HP Is that odometer miles or rebuild miles? First thing I would do is drain the oil and change all the filters including the fuel filter and coolant water filter. I would even go as far as to flush the cooling system and change the coolant with long life red coolant. If the coach has been sitting for a long time I would also put an algae killer in the fuel at the next fill up .FPPF "Kill It" is the best on the market. Trust me on this one, we were plagued with algae a couple of times. Along with that add FPPF 90100 fuel power diesel treatment. That will suck the water out. The algae needs water to reproduce. At 100,000 miles that engine is just over being broken in!
I have never seen a Cat that old with 100,000 original miles on it. The best thing you could do to diagnose any possible problems, if you are worried is to take an oil sample when you drain the oil and have it analyzed. We do oil samples at every oil change and you can really see what is going on inside the engine. If you know the miles since the last oil change that is helpful but without it they can still test it We use Fleetguard Oil Analysis kits available at most truck dealers. That will tell you if there are any issues with ring wear, crank wear, fuel in oil, water in oil, soot and a host of other potential problems.