Performance in debug mode (F5) vs. no debugging (Ctrl+F5)

Question

Hope you guys can help me with this problem: My C# app performs almost 3x as fast when I run it in Debug mode (F5 in Visual Studio 2003) as when I run it without debugging (Ctrl+F5). I would think that running in Debug mode would decrease the performance, but in this case it is actually faster. In any case, the difference in performance numbers is appalling to me. The app is a server stress tool that spawns multiple threads to simulate multiple users hitting the server. In Debug mode, it stresses the server to 100%. Running without debugging, the server CPU counter can only get to about 35% at the highest. Any help would be greatly appreciated! Thanks!!