what he said.... ^^^ i've been told that 3 being run at 450-500 hp will handle that power but may need refreshing every year or two. member from another site runs a tts kit that is the rough equivalent of a 3 and he is (correct me if i'm worn) somewhere between 550 and 600. he refreshes his once a year/season. go with a 4 if you can afford it. i personally have spent some time in a 600hp lmm that is wearin a sc4. that thing clicks off the shift like a stocker does to a stock dmax. hard to believe that the truck is 600 hp with it bangin gears as smoothly sa it does.
i personally will be doing sc4... soon i hope

.... peace of mind, not to mention i beat the thing like redheaded stepchild....