Stored Procedure is fast, report is slow.

I'm at the end of my rope on this one though and thought I'd ask if anyone has a clue for me.  

I've got a transaction detail report that runs really pretty fast (under a second) if you run just the SP.  There is no code in the report, but when you run it from Visual Studio, it takes literally like ten minutes.  I'd love to know what's going on.  I've done some googling, and it sounds like reporting services does some weird things with parameters, but none of the ways I've tried to fix it worked.