Averages don't give you the whole picture. NAFTA puts downward pressure primarily on low wages, not high wages. As a matter of fact, it may well lead to growth in high wages. Disproportionate growth of high wages could by itself explain rising average wages. These averages will not account for the decreased well being of lower wage workers.
Furthermore, average wages, along with productivity, rise over time. The time between now and when NAFTA was passed saw some of the largest rises in wages from unrelated factors. NAFTA's relative downward pressure on lower wages is real, and is not reflected in long term average wages trends.
We manufacture and export more than ever. So much for free trade doing what you claim.
Yeah, yeah. Go get another beer. 