your sure your engine mount isnt flexing and putting everything in a bind? And say if you were going 6k in first, push in the clutch and let the rpms come down, then try to shift into 2nd, have you tried that? As the rpms come up the pressure plate fingers push out harder towards the throw out bearing. If the clutch is adjusted to tight it could cause a bind in high rpms.Also if the engine mount under hard acelleration is streching, it will bind up the equalizer bar and jam the throw out bearing fork hard onto the bearing causing a bind on the input shaft collar. Causing the throw out bearing not to slide on the collar. You ever see a trans with a worn collar? I am just telling you things I have learned by personal experience. It may not apply to you. Also those plastic pieces are in good shape? If one fails it will , it will bind under accelleration