It sounds like if you declined, it's YMMV what happens from that point on. If Tesla had a plethora of vehicles, you would be good, but there are some reports where they declined (as in above post) and still haven't gotten an EDD yet.
You also risk losing your FedChoice loan as well. Tesla might delay delivery dates longer. I know you have 60 days to finalize the loan, but given recent rate changes, and now everyone is trying to get in on FedChoice since it's still much cheaper than other loans even after the increase and likely to be bogged down, I would jump on it ASAP instead of waiting it out. FedChoice will probably find ANY excuse to give you a higher interest rate, since you haven't signed anything. They're already losing potential money with each passing loan they get since their interest rate is lower than Fed Funds rate.
When I bought houses, I had to sign documents to lock in the rate. Since FedChoice has not actually had you formally sign any documents, I would really try to get everything signed now to ensure you got that rate. I found it already sus that they would only give you the rate over the phone, and not something like in an email, which to me, tells me that they can change the rate at any time before formally signing documents.