08 Denali Nav won't clear old memory

[chevyron64]

I bought a used 08 Denali with the touchscreen navigation system. I've gone into the saved addresses from the previous owner and deleted them all. the next time I go to navigation, they're all back. Also, every time I go to use the nav, I have to change the search area. Lastly, the clock is always 1 hour off after I turn the truck off.
Has anyone else experienced this? Is there a battery to store the memory in the unit?
Lastly, the manual says that every 50 times I use the navigation, the safety/liability warning screen will come up. This screen comes up every time I use the nav.