This is the Borg-Warner T5 five-speed transmission. When the roller-tappet 5.0 engine was introduced in the Mustang, it came with the World Class T5 designed to handle the 5.0’s increased torque and horsepower. Make sure you’re getting a World Class T5. Two types of World Class T5s are available--M-7003-A with a 2.95:1 First gear and max torque of 305 lb-ft, and E6ZR-7003-FB with a 3.35:1 First gear, which can take less torque at 275 lb-ft. Used, these guys fetch between $400 and $600. New from Ford Racing Performance Parts, and available from many Mustang & Fords' advertisers, they're around $1,500. If you're buying a used box, open it up for a look inside. Rebuilding costs can be expensive.