John, Since we bought the car Oct 21, 2007, it's never been warm enough here to see Tav temps as high as you report. If car does sit long enough, Tav and ambient are one and the same. But off for less than 8 hours, if Tav was like 77-78F, in my attached garage, it might still be 10deg F warmer than ambient - The HV battery is slow to cool

I don't have the NAV system, so can't comment on that. Sorry! I rely on SGII a lot.