Definitely sounds like you have an issue with some slippage on your 6R80 A/T equipped Mustang. Doubt if you'll get many replies to the issue here on this forum. However, since all 15-18 model Mustangs equipped with the 6-speed A/T transmission utilize the same model (6R80) you can pretty much do a search of all the Mustang websites and see if there's someone out there having similar issues with the 6R80 in their GT or V6 model.
2016 Ecoboost Mustang
2009 C6ZO6 - Katech Stage 2 #115
2005 Mustang V6 (Sold)
2003 Terminator (Sold)
2002 Mustang GT (Sold)
Last edited by Uncle Meat; 01-25-2018 at 10:21 AM.