Diesel performance is an endless cycle. What begins with the most powerful box-stock light-duty trucks on the dealer showroom soon turns into a dog fight between parts that deliver more fuel and parts that fl ow more air. A $400 tuner, $300 intake and $700 exhaust has led to a $4,000 motor build, $5,000 trans build and $4,500 turbo setup on more trucks we've been around than we care to admit. And it's all done with one thing in mind: turning wheels.