I have an ipad2 with 3G when the 3G is turned on and in the house but out of range of the router the ipad gets a but mixed up in what it is connecting to. 3G or house wifi. So I turn the 3G off. The only other thing that slows mine down is if I don't clear the history on Safari.
The only other fix I know is in Safari open up about. 6 different tabs then pinch in the screen & it will go to 6 windows. Tap ion one of the windows & you should be speeded up. But try clearing everything first including your emails using safari.