navagation devices used on trips

I have a 2015 Silverado that has in dash navigation. The database is at least 2 or more years old. As of yesterday Chevrolet did not have an update available and if they did it would cost $200.00. I purchased a Garmin Nuvii with lifetime updates for a lot less. We have programed both units for the same destination and have come up with different routes. That's just the way it is with GPS. I use a paper map for the big picture and the GPS for homing in on the destination.