I could screw up the distribution even more. Also Kaplan:
Diagnostic: 40
Highest practice: 41 (lowest-37; avg.-39)
Actual MCAT: 43
onmywayRN, a lot of my students score in the teens on the diagnostic as well. My experience is that most students don't score over a 20 on the diagnostic, no matter what the TEL says. I'd say that the avg. diagnostic scores range from 15-20; people commonly get three 5s or three 6s to start, not three 7s. So don't feel bad; your diagnostic score is completely normal, especially since you were missing several of the pre-reqs when you took it.
medhacker, I think it is true that the Kaplan tests require much more calulation than the real MCAT does. If you want to get some idea of what the real PS section is like, get a hold of one of the AAMC practice tests, and give it a try.