That's really low miles, not a good thing in a vehicle that's 24 years old. Have a mechanic check belts and hoses, air springs, etc. Tire age can bite you for a good hit on your wallet, check the date of manufacture,
http://www.tirerack.com/tires/tirete....jsp?techid=11
RV tires age out (about 6-7 years) before they wear out. If you want to be through, you could have an oil analysis done. An oil and lube, with all filters changed out (oil, fuel, air, transmission) could easily be $300 or more. The Cummins 5.9 and Allison transmission is a great combination, but if it's like mine, the transmission doesn't have a lock up torque converter, so no engine braking going down a mountain. With a VIN number, engine serial # and Transmission serial number you can learn a lot about the equipment on the websites of Cummins, Allison, and Spartan.
The engine is probably pure mechanical, no computer. I believe a '91 is before the issue with the 53 engine block, Cummins had a bad batch of engine blocks made in Brazil that had a large 54 cast in the block that were found to split and leak oil.