This is a very common problem on Freighliners with the MMDC. If you've got the MMDC, go to the "diagnostics" menu, the password is 8127. Scroll down to an item that says "odometer compare" or something like that. It will show you what what is recorded in the ECU and the IP.
Most say Freightliner won't do anything about it. Mine odo dropped to about 62k from 115k a few weeks ago. I'm not going to do anything about it except disclose the real number if/when I sell the coach.
Rob - Solo Full Timer
2017 Winnebago Travato 59G
Former 2006 Mandalay 40E