I think that the AAMC exams are a lot easier than Kaplan full-lengths, at least on the PS and BS sections. In fact, I had a little trouble adjusting to the AAMC question style and grading scale because I was trying to read too much into the questions (as you have to with some of Kaplan's stuff).
Kaplan full-length scores (in order): 28, 31, 32, 28, 27
I got concerned about the downward trend so I took AAMC 7 last Wednesday: 8 PS, 8 VR, 10 BS
I thought PS was fairly easy, but I realized that you can't miss nearly as many. Verbal really put a scare into me. I was freaking out at that point.
Yesterday, I took AAMC 6R. I made a 32 (11 PS, 11 VR, 10 BS) and that was without having time to finish PS or VR - I had to bubble in three or four random answers at the end of both and didn't even get to fully read the last VR passage. I was one question away from a 12 in PS, and two questions away from a 12 in VR.
I say all that because I was questioning whether I should even take the exam this Saturday, mostly due to my downward trend on Kaplan exams and a poor performance on AAMC 7. I realized after going over AAMC 7 that I made some dumb mistakes and even misread a few questions. Take AAMC 6R (or even AAMC 6 if your center doesn't have 6R, because it's exactly the same as 6R except for 5 more verbal questions). I think it will boost your confidence like it did mine, and give you a good idea of your score on Saturday since many people had similar scores on 6R and the actual exam in April.