Don,
The Transynd fluid change recommendations that Allison list for your transmission are;
General service- 300,000 miles or 4 years
Severe service- 150,000 miles or 4 years
Filter change at;
General or severe service- 75,000 miles or 3 years
Personally I just use the four year time frame for fluid and filter change, so that they are always changed at the same time. That makes it easier for an old person like me to remember.
Gerald