Brian, what I like to do is seal the new seal onto the pan with gasket
sealant and then let this dry.  Then install the pan so that you know the
seal is held in place.  Also be sure that your new seal is oriented properly
as it can only go on one certain way.  If you put it on the wrong way this
could also be causing your problem.

Thanks,
Ken Wilford
John 3:16
www.vanagain.com
Phone: (856)-765-1583
Fax: (856)-327-2242