Truck Repair: brake problems, dodge dakota sport, piston cups

Question
I have a 1998 Dodge Dakota Sport heavy duty.MY problem is with the brakes.When I press down on the brakes they are normal,the next time I hit the brake pedal it goes almost all the way to the floor,if i let up on them and press down again i have full brakes.I have blead them thinking of air in the line NOTHING.I even replaved the Brake Booster and still no change.Their is no brake fluid loss
 Where do I go next?
                     Thank You
                     Henry

Answer
Hi Henry,
If there is no fluid loss, the problem is either the master cylinder leaking back past the piston cups, or an antilock brake valve leaking.
I really expect it to be the master cylinder.
Replace it with a rebuilt one, rather than trying to repair your own.
Van