Here is the brochure:
At this point it's all about prior maintenance. If records are available, go over them in detail.
1. Oil/lube/filters annually
2. Allison transmission may have shipped with Dex III or Transynd. Should be Transynd now.
3. At least annual check of SCA level in coolant.
4. Air dryer service every 2-3 years.
5. Front wheel bearings serviced a couple of times.
6. Tires should have all been replaced by now due to age.