The motorhome that I just traded had the same situation about a year ago. I had just had the transmission fluid changed, we were traveling on an interstate and stopped at a rest area. As I was walking around the coach, I noticed some fresh fluid underneath it. When I crawled under, I found it was transmission fluid. I panicked, located a Cummins facility in the next town and headed there. If was after hours when we arrived, so we stayed there for the night and the next morning they checked it out. It was determined to be coming out of the breather tube, a result of being overfilled and very hot.
The tech said it wouldn't hurt anything and would settle down as soon as enough ran out. It wouldn't leak all the time, but it did two or three times after that and then nothing. I drove it 5-6,000 miles after that and everything was fine.
2007 Tourmaster T 40 A
Toad - 2011 GMC Sierra 4X4 extended cab