If you haven't done the tundra brakes - skip it. Save your $, buy GOOD QUALITY rotors and have a full rear brake service done either by yourself if you really know what you're doing, or a knowledgeable pro. There's a reason they all start getting bad at 150k. It's not because the front brakes are under sized - they are more than adequate. It's due to a combination of cheap after market rotors and the rear brakes not being adjusted and not helping with the braking. Fix the rear brakes and you'll fix the problem.
I have tundra brakes on mine. Yes they are bigger, but only a small amount. After going through this, I'm convinced that the rear brakes are where you should spend your $. The factory fronts are more than adequate size wise. They're bigger than the brakes on thousands of solid axle trucks with way bigger tires - my FJ40 has smaller discs and stops 38's without issue and weighs about the same.