How to solve psp iso/cso game lag?

i am using prome-4...i have format my psp but it still lag...i have change the clock xmb and game to default and 333/166 but it still same... i also had change iso video amout to m33 driver and sony np9660 but it still same... can anyone help me how to solve this problem...my memory card is not fake.i'am sure about it..