Most people don't do enough untimed practice, and I think that's where the most improvement happens. OP sounds like he's got the hang of the questions, so its now just a matter of converting that to pattern-recognition, and killing the test under timed conditions.
Many tutors and classes require students to do a timed preptest (or show an actual test score) up front, so that there is a somewhat objective measure of improvement. This has a lot to do with score guarantees, and general covering of asses. It's also great advertising when you can say you helped someone improve 20 points.