So i'm fighting Darth Vader on Apprentice difficulty and i find myself loosing everytime i get into a saber lock or get force gripped.  The force grip part is especially annoying since Vader does it ALOT and no matter how hard i mash the button i can't break free.

Has anyone else had this problem or is it just me?

Did you check out this guide?

Beating him isn't the problem but whenever he uses force grip on me i can't break free.  It's like the game isn't recognizing the button mashing which makes the fight really annoying.

He won't Force Grip you if you don't jump on to the center platform he's on (I'm assuming you're on stage 2 of the fight here). Essentially Vader's Force Grip is inescapable, so if you get caught, don't bother mashing and just wait until he releases you. He's weak to lightning combos including the Sith Saber Smash and lightning grenades. You should be able to beat his saber locks if you mash hard enough.