Ive had it happen. Usually reload the tune and it came back. It is caused by a solenoid IMO, eventually you will get a code. Ive driven mine in 4th for a while when it would lose OD. Ive done solenoids in my 6.0's 5r and it wasnt bad, just messy.
a built bts fixed mine...lol.
a built bts fixed mine...lol.