It's beeen a while, but the PFT in the 1986 was:
20 Pull-ups
80 Sit-ups in 2:00 min.
3 miles in 18 minutes
This would net a perfect score of 100.
The best I could ever muster was 20/80/19:00 flat.
That long arsed run along the fencline of the airport around MCRD/SD...

The mental stuff is so true - be prepared for it. You will screw up, you will be (figuratively) beaten down, and you will not be fast or smart enough.
Then something happens, and 3rd phase rolls around, you start to click and think you'll actually make it. They build you up; and into a United States Marine.