Decades ago, Ford made the jump from four-speed manual transmissions to five-speeds. Newer Cobras even feature six-speeds, so it’s natural that those who own earlier Mustangs with four-speed manuals now feel a little gear envy. Many people love the feel of having a manual transmission, but if you’re still using a four-speed, you’re missing out on a lot of performance and economy potential. Adding a transmission with additional gears places your gears closer together for better acceleration and gives you more gears to choose from for easier cruising. But which transmission is right for your Mustang? You need one that’s strong, smooth and capable of bolting to your engine, and it’s not easy to find all three attributes in the same gearbox.