"3 When you loaded the TC, if the front and rear of the truck dropped the same amount, the COG was over the rear axle."
In theory, if the COG is over the rear axle, the front should not pick up any of the load. And both your trucks should have the same bed length to rear axle relationships. The longer wb truck will carry more of the load on the rear axle, but if your COG is 4" ahead of the rear axle in both cases, your front springs will always pick up some of the load. 60 lbs and 4" isn't much, so the variables of scale accuracy and cargo placement within the camper may be having more of an effect than anything else.