I was going about 4 MPH more than what Waze was saying. Not too bad.I had same issue using waze then realized that when plugged into Apple Play the speed reported in the app is off the speedo and not GPS. I unplugged from Apple Play and the Waze reported speed thru the app and on the iPhone rather than on the Uconnect screen mirrored my GPS enabled radar detector and about 10 MPH different than speedo at 75 MPH reported on Speedo, net net GPS = 85 MPH. This is not a linear relationship and the delta smaller at slower speeds.
Fun fact, the KO2 37" tires will pull the speedo below actual speed and thus allow shooting beyond the speed limiter since the limiter is tied to speedo which is now inaccurate unless recalibrated via Taser Mini/AEV module, etc - so I am told and speaking hypothetically .