904 tranny problems

So If I have to take my tranny apart I should go with a complete rebuild kit I'm guessing and while I'm at it would a manual valve body be the way to go, and what type of rebuild kit should I buy.
Remember was rebuilt around 5,000 miles ago but I am pushing 470 HP and 500 ft. lbs. of torque now but not putting on slicks and drag racing it just a road car to play with.
Glad you guys are here to help me figure this out. Thanks...