I have searched regarding my issue, and haven't managed to find an identical problem.

When I start my vehicle the screen comes up fine, and if I agree and continue, I see the GPS, and my position is correct.

Now, if I start driving, it will take upwards of 3 minutes for my GPS to finally realize that I have started moving, and then jump about a quarter mile at a time (DIESEL!), until it catches up to me.

The same thing happens if I start the vehicle, get into my Nav, and try to enter an address. It will not allow me to do anything for a few minutes, but then after it starts moving, everything works just fine.

I also do occasionally get Nav Failure popups, even if I let the screen go black. New nav time?

 

Try cleaning the DVD and reading lens on the Navi drive in the trunk before considering anything else.
Cleaning pointers are in this thread: https://acurazine.com/forums/3g-tl-audio-bluetooth-electronics-navigation-94/diy-how-fix-navi-disk-read-errors-873489/.

Welcome to AZ.