well, both words predate the truck in truck-farm--it's rather complex, which is why I didn't post it in the first place, but let me see if I can boil it down:

truck(1) [barter] stems [ultimately] from OF. trocher, in med.L. trocare, to barter

truck(2) stems [ultimately] from Gr. trochus(?), to run (the motor vehicle is just one of many senses, e.g., the wheels on a gun carriage, a wooden-block on a ship's mast, the axle on a skateboard, a dance...)

now, I'm not sayin' there's no [ultimate] connection between the two, but it would seem to go back a ways.