You set the Can Shrink property of the controls AND of the Details section?
Is the gap the same between every record, or does it vary? From what you
have said so far I gather that it varies. Does it occur between records on
the same page? Do all of the records use the same amount of vertical space
on the page?
In report design view there is a drop-down box on the formatting toolbar
that lists all of the controls on the form. Make sure you can account for
everything on that list. Other than that I can only suggest that you add a
back color to the Detail section and to any headers and footers, as well as
to the controls. You need to find out what part of the report is taking
extra space. I know of no way other than detective work. That's not to say
there are no other options, but this is all I can suggest unless there are
details you have not mentioned.