I had a similar problem and it wasn't just physically sitting that long (my back starts to hurt after about an hour), but also that I wasn't reading the questions as sharp after 100 questions or so. I mentally broke the test into 4 x 50 question banks (in my head) just so I didn't get overwhelmed and notched my scratch paper for every 50 I did. I took a couple of minutes after each "bank" to just take a deep breath.
Secondly, I'm the worst test-taker in the world, so really used the precast to hone my test taking skills to be as efficient as possible on each question, but regardless its a slog. As I understand it the PMP test difficulty can vary between applicants, but the scoring adjusts accordingly. With that said, I finished the first section with plenty of time. The second part of the exam had very long winded questions, so I didn't finish with a much time to review (maybe 15 minutes).
My approach:
1. Take the tests at the same time of day as your examination.
2. Approach the test with the same "game time" approach as you would for the examination.
3. Have a marking strategy so you don't get bogged down on any single questions.
4. Jot down how long it takes you to do 50 questions, 100 questions, 150.
When training for a marathon you never do an actual marathon, but you do many looonnnnggg runs to get your body used to the exertion. Similarly, you need to be able to train your brain to be just as fresh for the last 50 questions as the first 50. I imagine of lot of people fail by just a few questions, which were missed because they got mentally fatigued.