I don't know about MHs. but on pickup trucks you are advised to use the tow haul mode when ever you are towing. They put it on there for a reason, and I would tend to believe it's to safe guard the tranny.
Don't know if you are towing with your MH or not, but it might be good to check/ask your local Ford dealer. Not the salesman either. Go back to the service dept and ask the supervisor.
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