Slow iPhone 3G after iOS 4

Why is my 3G so slow?????????? I updated to 4.0 and my 3G has been having issues ever since. I really cant stand it! the rotation takes like 5 seconds, switching home screens is jumpy, the iPod crashes if you use the purchased link in the iTunes app. Folders open and close slowly, and when I lock it the lock noise plays then it plays like 3 more times. Settings also crashes!!!

is anyone else having these problems? Im really confused. It didn't do this with 3.1. I've also never done anything like jail breaking it....

I've tried restarting but nothing works, any help, Is it time for a 3GS?