The dealer did some troubleshooting last week, and found a small scorch mark on the thermostat circuit board. Thinking this was the problem, they ordered a new thermostat.
I brought the trailer back today for them to switch out thermostats...they had the TT 20 minutes and were done. They made some phone calls, put in the new thermostat, and then called AIRXCEL/Coleman when the fan still operated as before. And then we got our answer...
The tech gave me a copy of the installation literature from AIRXCEL/Coleman which clearly shows that in the "ON" position, the fan will only run at one speed, and that in the "AUTO" position, it will run at low or high speed.
The tech was concerned about that scorch mark on the circuit board, so although the unit was actually functioning properly it was good that we were able to have the thermostat switched out...and the dealer covered it as warranty work.