Another thing you might check is the adjustment of the rear brakes. I am assuming you have drums on the back.

My son was working on our old 4Runner a couple of months back and having similar issues. He had ordered the new master cylinder but was still trying to prove to himself that it was needed. (he is a mechanic)

It turned out that the rear brakes were out of adjustment - too loose. Once he tightened them up, it was back to normal.

Randy

1995 V6 SR5 5 speed 4X4 - 4Runner - dark blue