I'm not sure about a pre-sceen, but I do know that Mayo looks at MUCH more than MCAT and GPA. The second of half of your post is not exactly accurate. Everyone who applies gets a request for money, but this means nothing about your chances of interview. Once they receive your money, they begin to review your application (primarily activities) in deciding whether to request letters from you (you should not automatically send letters to them when you pay). Here's some numbers that have been posted in previous years' threads:
4000 apply
800 get LOR requests
250-300 get interviews
~72 are offered acceptances (including from alternate list)
personal statement is not read until after LORs are received.
42 MD-only spots available.