1) i NEVER read the question stem before the stimulus. thats probably the fundamental difference between kaplan/pr and testmasters/powerscore. the main reason why is that it wastes time(if you read the stem first, you almost always have to read it again after the stimulus so you end up reading it twice) and reading the stem first ruins your natural reaction to the stimulus.
2) everything i learned about logic comes from my testmasters class. memorizing sufficient and neccessary key words(unless, only, if, whenever, etc.) is really important, you want to get to the point where you dont even have to think about it. at first i would see the word "only" and i would have to think "hmm, does this introduce the sufficient or the neccessary, and does it negate either of them? what exactly is a neccessary condition?" now when i see the word "only" i dont even hesitate in reading it as introducing the neccessary and understanding what exactly it means that it is a neccessary condition in the stimulus.
3) testmasters was recommended to me by a lot of people, and everything i read about them online was positive. i took a princeton review SAT class in high school and wasnt really happy with it, and i heard mixed reviews about kaplan, so i figured testmasters was the way to go.