John - I've got exactly the same trouble with my '58 Apache half ton stepside 235. New battery, new starter brushes, armature cleaned up, clean and solid connections.The starter works fine on the bench, but on the truck it struggles to turn the engine over and dips as if the battery is flat. It has gradually got worse and now won't start at all. I could try a new starter but like you I bet it'll make no difference. I hope the forum can solve our mutual problem.
