JWalker,
You've discovered the real "pot of gold" that few have discovered. The truth is, there's really no limit to TranSynd drain intervals whether you're measuing in miles, kilometers, or calendar time as long as you're running oil analysis. It states this in Allison service materials (I'm the guy that wrote it). The transmission oil analysis will tell you two things. First, it will tell you how the oil itself is holding up by assessing the amount of contamination, viscosity change, and oxidation change. Second, it will assess how the transmission has been responding to the condition of the oil by assessing wear metals. It's no different than a visit to your doctor to get a blood test to check your cholesterol and/or blood sugar. Oil analysis is the way to go to maximize your oil dollars.
Hope this helps. You can pass this on to others.
