It doesn't happen often for me and when it does; it usually resolves itself after a few restarts. Unfortunately that doesn't seem to happen for you. Has the window animations ever been 'normal', or has it always been slow?
How many other apps do you have going at startup? Perhaps a particular start-up item is conflicting with the driver
initialisation. Maybe try temporarily disabling other start up items to see if it has any impact.
Apart from Darkxeno's advice of re-installing the drivers
, I honestly don't know what else to suggest.