Speaking of the T5's durability, this gearbox has garnered a reputation as being wimpy and incapable of handling the power of a typical street machine. In truth, the better variants of the T5 can handle a healthy V-8 just fine-until it comes to full-on power-shifting, particularly with sticky tires. In those situations, the pinnacle of T5 development may be necessary: the G-Force T5 (see G-Force sidebar).
Tremec/TTC 3550/TKO The Tremec gearbox has the appearance of an OE-designed assembly, yet most of its uses have been in aftermarket applications. Primarily built as an upgrade for Ford manual transmissions, the initial version of the Tremec 3550 used a Ford "Toploader"-style bolt pattern and center spacing merged with a 10-spline input shaft and a 28-spline (Ford C4-type yoke) output. Thanks to heavy-duty features like tapered roller bearings for the countershaft and caged needle bearings under First through Third gears, the 3550 carries a 350 lb-ft torque rating. The next evolution of this gearbox is the TKO, which has a 425-lb-ft torque rating, due mostly to its 26-spline input shaft and 31-spline (Ford C6-type yoke) output shaft. The TKO II is further upgraded with gearsets made from higher-grade steel, raising the torque rating further to 475 lb-ft. The TKO II can also be had with a 0.83:1 ratio in Overdrive, which many road racers favor since engine rpm doesn't drop dramatically in Fifth gear, often permitting the use of Fifth on long straights.
One of the features of the Tremec gearbox that makes it favorable for swapping is its multiple shifter locations. There are three possible shifter locations on the gearbox, though each position requires a specific shifter. Most Ford applications used the rear mount, and this is the position most aftermarket shifters for Tremec are designed to fit. However, since many muscle-era cars are better served by mounting the shifter in the center position, many of the outlets for swap kits offer center-mount shifter hardware.
There are now Tremec gearboxes available for applications other than Ford, including GM and Mopar. Some of these are factory-produced while others are modified after production. If you're considering a Tremec swap, make sure to find out exactly what you'll need to complete the job, including any modifications that may be necessary to accommodate shifter positioning, transmission crossmember modifications, bellhousing and clutch requirements, driveshaft yoke and length specifications, and speedometer cable/gear adapters. Currently, there are a number of very complete kits on the market to simplify Tremec swaps for various applications.