Sitting still, pumping the brakes it's fine. Engine running and pumping, feels fine. Hit and hold, holds a firm pedal. Light touch and hold, it's firm. Pull it into drive, ease off so the truck will roll a foot, then reapply, goes right to the floor. Is this an ABS thing? Why is it fine and then roll it forward a touch and it's going to the floor? Fluid level a touch low but not out of the norm? Front brakes are worn but 3/16" left. They aren't on the backing plates. Will get them replaced this week. But why does the pedal dive when you go forward even a foot?