Navigational (global Positioning System) Gps problems of the 2005 Chevrolet Trailblazer

While traveling we noticed the we were being passed excessively, we looked at the speedometer and saw that we were doing slightly above the speed limit. Out of curiosity we checked our speed against our gps / Smart phone and saw that we were doing 30 mph under the speed being reported by our speedometer. After searching on the internet we found that 100's if not 1000's are having the same issue or even sometimes in reverse where it states that they are doing 120 mph when they are only doing a fraction of that. In addition we have found that there has been a recall on this same part on other gm vehicles for the exact same reason but the Trailblazer was excluded for whatever reason. How can not knowing how fast your actually going not be a major hazard especially with a proven history of failures.