Playing devils advocate here....How much overweight are we talking with the current combination? If you haven't weighed the trailer with all the items in the box, people, etc for worst case scenario, you may not be extremely overloaded. If it were me and it was 3-400 lbs and I towed the combination 10 times a year, I would keep the Tundra. My trailer is similiar in size/weight, and I have had the pickup box filled with wood, generator, etc, and towed up 13 mile long hills gaining 6,000 ft in elevation multiple times in 105 degree heat with no issues. Just a thought....