I just picked up my MYP on Tuesday 03/01, and drove it 400 miles from SLC to Bozeman, MT. For perspective, my wife has a 2019 Model 3 and I have driven that car a lot using both TACC and autopilot, so I have a good basis for what to expect from both of these systems.
I drove manually through most of the traffic in SLC, but once I got north of the city, I turned on autopilot. Traffic was very light, and I was set to the max speed of 80mph. I was slowly approaching an 18-wheeler in front of me, and noticed that another car was approaching from behind. The timing was such that I could maintain my speed and the approaching car behind me would likely pass before I needed to change lanes to pass the 18-wheeler. When I got about 5-6 car lengths behind the 18-wheeler the MYP slammed on the brakes. Not a gentle slowing but a full panic stop. The approaching car behind me was close at this point as well and had to quickly respond to avoid hitting me. We 3 vehicles were the only vehicles on that section of road, so not a confusing scenario. I quickly hit the accelerator to halt the braking, but the guy behind me was angry (justifiably). I wish he knew how angry I was too.
For the remainder of the highway driving, this same thing would happen when I approaches 18-wheelers to pass. I had to cover the throttle to overcome the braking response. I would say it was 50+% or more that the car would respond this way.
Additionally, I would also get slowing when an 18-wheeler was traveling on the opposite side of the highway separated by a large median. The truck was easily 50-60 yards away, but the car couldn't figure it out and slowed down.
I also experience a few false alarms where no object appeared present but the car would slow or warn that I was about to hit something.
All of this did not make for a peaceful experience or engender any pride of ownership in my new purchase.
Once I got on 2-lane roads, it was more of the same. Every large truck that passed in the opposite direction would cause slowing or a hard brake. This was with 75+% of the trucks that I passed. I had to babysit both systems to such an extent that they became more nuisance than benefit. If the roads weren't so empty, I never would use them for fear that someone would hit me from behind when the car braked.
TACC and autopilot were both un-usable for this trip and IMO downright dangerous. This new MYP is nothing like the TACC and autopilot performance of my wife's 2019 Model 3.
I contacted Tesla upon getting home regarding these issues, and I received what appears to be a standard "legal" response explaining that this is a beta feature and that there are limitations to the performance of the software. I received no recognition or concern for my problem, and no path to any form of solution. I basically have a new car that doesn't have a functioning cruise control.
Note that my car was delivered with 2021.43.102 code, so I'm cautiously optimistic that things will improve when I get an OTA update.