I wouldn't play Diamond Dynasty, ever, because that mode just doesn't appeal to me at all. Same as in NHL, I won't play that stupid collect cards ********. RTTS and Franchise mode are what I stick with.
I never experienced any of the problems you're talking about...have you downloaded the most recent patches? I actually pre-ordered the game and stayed up until midnight on the launch day to play it though and I never had any issues even then. Maybe your sliders are screwed up or something?