Navigation System Malfunction

[ddawg9191]

I took my Lexus ES 350 to Chicago this summer. All aspects of the nav system appeared to be working fine. On the way home I noticed that the time calculations were not matching the distance I needed to travel. I understand there is a setting for standard highway speed etc. but the time don't match those settings either. For example, my setting for highway speed is 100 km/hr. and if I have 100 kilometers to drive the nav system is telling me the trip will take 1 hr. 45 mins. There is no city driving calculated into this. It is all highway. Has anybody else experienced this? Any suggestions? Just take it to the dealer or am I missing something here?

Any help appreciated.