The 1966–2004 Ford C6 three-speed automatic transmission still finds a home in restored muscle cars, nostalgia race cars, and heavy-duty towing apps. Like any old-school trans, a good shift-improvement kit yields more positive shifts and tire-chirpin’ gear changes that improve full-throttle acceleration. For the vast majority of consumers, a smooth-shifting automatic transmission is the gold standard. Detroit caters to the least common dominator, except in the relatively rare high-perf models. But with a hopped-up motor’s higher torque and power numbers, smooth shifting means lazy shifting that can cause excessive clutch and band-apply times. And that can mean higher temperatures and burned friction material leading to eventual transmission failure. Assuming the transmission’s internals and frictions are otherwise still in good shape, the answer to this problem is an aftermarket shift-improvement kit. To a large extent, shift timing and quickness on traditional, pre-electronic transmissions is controlled hydraulically, through passages, orifices, springs, and check valves in the transmission’s valvebody. By modifying the valvebody, a bolt-in “shift kit” provides firmer, quicker ...