I just picked up my new Y Performance after doing the FSD transfer. I learned a lot from this process. The hardest part was timing the sale of my 2018 Model 3 LR. Your Model 3 has to stay in your account until the FSD transfer is completed. I ended up selling mine to a 3rd party car buying service yesterday afternoon. I kept the Model 3 in my account until I completed my delivery. I was told you can remove it once FSD has been taken off your current car, but I wasn't going to risk that. Everything was very stressful and you need to be ready for that if the sale of your current Tesla hinges on you being able to pay part/all of the current Tesla's cost. Otherwise, you'd want to plan to take out a temporary loan until you get the funds from the sale. Local dealerships were telling me it was going to take a month to get my equity because they won't release it until they get the released title after paying of the remaining portion of my loan. I went with a company that immediately wired me my equity after I dropped the car off.
Another issue I had was that the gallery emailed me the FSD Transfer Agreement and asked me to email them the signed copy so they could upload it. I did that and was told the FSD would be removed at the 72 hour mark. Nothing happened, so I asked Tesla and they said it was in process and not to worry. Another day went by and now we're less than 48 hours from delivery. I text Tesla again and that's when someone tells me that the form that was uploaded didn't have my signature. The gallery screwed up, so they electronically sent the form. It takes 24 hours for the form to process, so it finally got removed from my Model 3 less than 24 hours before delivery. Make sure you only sign an electronic form so you don't deal with what I did.
If anyone has any questions on about the process, let me know.....