Nothing has changed in the app itself to cause the speech rate to change, but I did run some tests comparing the speech result on iOS 8 and iOS 7 and it does sound about twice as fast on iOS 8. I have a new version of Walkout Song DJ prepared that I was just waiting to release until I had some feedback from people using it with iOS 8. There always seems to be some little issues like this whenever a new iOS version is released. I suspect I will need to add a speech rate setting on the app settings page to allow tuning the rate to your taste.
I appreciate the feedback. Please look for that new version in the next week or so. Hopefully, that will get you back operational again.