Burn Out?

Hi all I was wondering if anyone else had this experience. I just finished the PT's from PT's 42-51 (the red book) and I was averaging about 18-20 on LR. I just started PT's 62-71 (Purple Book) and I have done pretty terrible on the first four LR sections. Is there a huge increase in difficulty between the two books? Or am I just getting a bit burnt out? Or could it be something completely different? Not really sure what to make out of the situation. I was really confident before starting this book, but I am feeling really un sure of my skills now.