Sounds like your brakes are working about like they are supposed to work. I had a 69 chevy 1 ton that had to carry that "extra" load every once in a while. Just remember most trucks will "GO" down the road with a lot more load they can "STOP" with. Also, make sure those tires will carry the load. Your truck is a beauty!

Always get a 2nd opinion, especially if I am the source of the 1st opinion.