Often lose satellite signal when heading south??

Hello, you're chasing a phantom losing battle here, I'm afraid. There must be some kind of interference, but for you to figure it out and find it and then be able to resolve it -- it's just doubtful at best. Sure you could replace the antenna and try and troubleshoot the satellite radio receiver, but ultimately it could be a result of a change in the environment surrounding the vehicle where the problem is occurring. For this one, I'd suggest reaching out to your local Toyota dealership for assistance.