Fluid analysis, that's what Allison says. But they say compare your sample with an original sample (from an new trans, I guess). They say change fluid if the difference between the old and new sample differs by xx%, which is good advice if you have that original sample. They also say 300,000 miles or 4 years, whichever comes first. Just wondering what others do. We only put on about 3,000 miles per year on the Beaver. I had the tranny fluid replaced this year in my Jeep Liberty, shifts like new now.
