iPad 1 is slower after upgraded to iOS5

Since upgrading to the iOS5, I experience a big drop in performance on my iPad1 3G. The tablet is noticeably slower. Apps no longer switch quickly and some apps are not working. Mail app takes a long time to load new emails. Delays in gestures and safari. Reinstalling the iOS and still get the same issues. The iOS5 is almost unusable.The lowest devices often seem to lag and sometimes severely