6R80 downshift issue 6th -> 5th 2015 Mustang GT

[caniggia]

Near 180km/h = 120mph at 3600 rpm its not possible to accelerate. I need to select the 5th gear but this is not possible over 170km/h with a ecoboost.

There are 3 tables in Shift sheduling, downshift prevention, enter last row 250 in all 3 and you will be able downshift from 6th to 5th at any speed bellow 250.
Entering higher values than 250 does nothing and it's not resolved. No problem to pull 5th to max speed you can.
Could be not all EB calibrations has this tables added, i requested sometime to add in EB and v6.