McGraw's PCAT book is plain awful. Math was way too easy and chem was pretty insane. However, the chem section did teach me something.
The gen chem section seemed to all have a gimmick to solve in under 37 seconds. Look at a ratio or some clue to avoiding making calcs. If you ran out all the calculations it's impossible to finish in under 30 minutes (more like 60 min). If you can spot the gimmicks, it will help in the real PCAT.
Also the McGraw org chem was insanely hard in my opinion but the good news it doesn't seem to match what the Pearson practice PCAT exams ask for so whew!
I did both Pearson practice PCAT chem sections barely using any scrap paper so there were no intense calcs, maybe 1-2 questions tops. Even then, you could almost eyeball the question and run the numbers in your head on most of those. Amazingly, I had time to go back and doublecheck all the questions.
Bottom line, use the McGraw chem section as a test of spotting the gimmicks. And practically ignore all of the org chem questions.