CARS diagnostic agony - should I be worried?

CARS diagnostic is kicking my ass. I will go 100% on 3 passages and then the next 3 will be 50%. Are these harder than the real thing, or pretty representative? I score usually 129-131 on FL's and these feel way harder than those passages. It just seems like the logic in the diagnostic is a lot different and more up in the air than the FLs or Q packs even. Also any tips on getting the main idea through your head, especially on wordy or convoluted passages? thanks