Hello David and thank you for your post.
I have a tf mini installed also as a forward sensor, only in my case so far i had taken power from the GPS cable hack.
In this post TF-Mini-Obstacle Avoidance Issue 3.5.5 i have described an issue i have had with it in GPS navigated mode.
Have you come across anything like that?
Dear Siya, i hope you can look into my post also.
Thanx in advance for your time!