I found the Kaplan tests to be much harder than the AAMC tests. Yeah, the curve is very generous on the Kaplan tests, but that's a reflection of the brutality of the tests. The passages are far longer on the Kaplan exams than anything you'll see on AAMC tests, both practice and the real thing. They're also a lot more complicated, and the questions are really, really hard, especially in the PS section. The nice thing about Kaplan is that after you've gotten used to their tests the AAMCs feel really easy.
Something to be aware of with the Kaplan exams though is that while the more generous curve is meant to offset the higher difficulty, it can inflate your score if you're the kind of person who guesses on a lot of problems. The AAMC exams give very little (if any) tolerance for guessing on problems, whereas the Kaplan exams with their large score ranges and low thresholds for getting good scores almost reward guessing.
FWIW my average on the Kaplan tests I took (1-4) was 32 IIRC (too lazy to look up my old posts to find out for sure) and ranged from 28-36. My AAMC average before the Kaplan tests was 33, and my AAMC average after the Kaplan tests (I took the four Kaplans between AAMC3-7 and AAMC8-11) was 37. I ended up with a 39 on the real thing, which also happened to be the same score I got on my last AAMC practice test.