ok one more time but this time try to pay attention. Your muscles could need a change in workout meaning a change in exercises, reps, sets etc. Not that you dont push hard that was never said. Shocking the muscles by throwing something new at it is what I meant. You may want to check your nutrition also to make sure your getting enough protein, but I really dont think that is it since your other lifts are going up.
Just gotta love people that ask for advice, then shoot down whatever advice they get. lol