IMO, the final drive mod is not really a thing. a lot of people think that they are cracking into their tranny to do this (I guess technically you are), but the final drive for the A604 is in a compartment on the drivers side of the trans. totally seperated from the internal workings. you only even lose about a quart of fluid doing it.
so if you have a reasonable set of tools (those sockets and steering wheel puller could offset the cost of labor to do this) and the ability to turn a wrench, I would suggest that YOU give it a try yourself. just read up on the write-ups.

and remember, we are here to walk you through if need be. just ask.

as far as the shift kit goes. I have had the valve body out before, and it is really simple compared to our turbo brother's transmissions. maybe not for the faint of heart though. it is true that if you get one done at a shop, you may as well get both done.


btw. when I posted $100, that was only for the final drive mod (not for the shift kit). I remember a few guys saying that that was what they paid,