The weight shifted to the front because with a lighter pin the truck was more level taking out the 1" dip to the rear it had with the heavier pin. Leveling the truck will always shift some weight to the front axle. This also works for those that use airbags. If I had airbags and used them to level the truck, even if the pin stayed the same, some of the weight would get shifted to the front once the truck was leveled. I never realized this until one of the moderators on the Ford forums I frequent did a test of his own. He weighed his truck/trailer as a package with his bags deflated and the rear sagging just a touch. He then aired up his bags to level out his truck and immediately drove back across the scale. He found the same as I did this spring that leveling the truck distributes more weight to the front axle.
To illustrate, here are two pictures from the two trips where I scaled my rig. Again the first is with the garage and tanks empty. You can see my truck is down a touch in the rear. The second is with the garage loaded and the fresh tanks full. The truck is almost dead level from having a lighter pin and thus has also shifted some weight to the front.
