The 5R55s trans has 1st, 2nd, 3rd, 4th, & OD. The 5th gear is the OD. If you switch off the OD, your top gear is then 4th. You may be feeling what you think are extra gear changes in 4th and 5th but it is only the converter lock-up function.
With a 5R55s, never punch it WOT in OD. It will kick...