I didn't write that clear enough. The car actually RESET the speed to those speeds and showed that NEW speed set on the binnacle. ie it showed 45mph as the set speed from 75mph and / or showed 65mph at three other instances. I had to bump the stalk up until I reset it to 75 mph again. It was NOT phantom braking at all.
Also that Interstate does not change speeds and has literally been there forever and non of our AP1 / AP2 / AP 2.5 or HW3 cars has ever changed speed from the set TACC or AP speed including the limited time I used NOA on my HW2.0 S and when I first picked up my HW3 car this year..
This is the "Fleet Speed" feature. What's probably happening is that your car thinks you took the exit you just passed. Happens to me all the time in my Q3 2017 Model S (HW2.5/MCU1) and hardly ever in my Q3 2018 Model 3 (HW2.5/MCU1). I have a case open with Tesla about it but it is very difficult to get them to pay any attention. I started a thread on this here: "Fleet Speed" (mis-)feature in 2019.8.6+