Has anyone ever tracked their speed with a gps? Excursion shows 65 and gps shows 61.With Gps inmy pickup it is.5 to 1 mph off, if that. Ford dealer checked setting and said that there was only two settings for tires and it was set to my tire size. They took it on and paced with ford f150 and said it was fine. I asked them, then why am I alway getting passed.