Even though my Silverado has the built-in navigation system, I have a Garmin RV760 LMT. It has steered me away from some roads that I was too heavy for. It is great for towing. I have or had GPS units from Garmin, Tom Tom, Magellan, Lowrance, Panasonic and DeLorme, and the Garmin units are far superior to any of the others I have used. I've only gotten rid of one GPS. It was a Magellan that was so horrible that I gave it away.
2013 Silverado 2500HD LTZ CC 6.6L Duramax Diesel
2014 Sunset Trail SF270BH
Holly & Buster, mini Dachshunds
2016: 1 trip, 3 nights in 1 state, 316 miles
2015: 5 trips, 18 nights in 3 states, 2707 miles
2014: 5 trips, 14 nights in 3 states, 2426 miles