SSRS query performance (dynamic SQL vs. stored proc)

In SSRS 2008 R2, I have a query that runs in 5-8 seconds in SSMS. When I run the report it takes about four minutes and when I run the same query in Report Builder's Query Designer it takes about four minutes. (db, query, SSRS, all running locally)I turned on profiler to capture the activity between the query run in SSMS vs. the query run in SSRS and I see that SSRS puts my query in a string and does an exec sp_executesql command. Is it the dynamic SQL in the sp_executesql that's giving such a dramatic performance difference?If I change the report's data source to a stored procedure would that eliminate this seeming overhead?Thanks,Rob