Is the Gospel flat 5 slam a real concept and is it to do with when you move to the IV chord via a flat five? Like in this Chakha Khan recording at ~3:56 https://www.youtube.com/watch?v=mMhulkKXQjY&feature=youtu.be&t=3m55s

Asking for a friend
yep that's the one. and the bass player is right in the shot too, nice