The T56 has two overdrive ratios in most cases.

The Tremec is often preferred by the high torque crowd. It was originally designed as a truck trans, so is plenty stout, and a bit sluggish on shifts. If you're not trying to speed shift to the traps it shouldn't be an issue. This is a real popular trans with the Mustang, and Cobra replica crowd, even the big block boys. One advantage with the Tremec is that there are three different locations for the shifter, not only one as on the T5, so you can chose the one that suits the spacing of your car. The rear position, which is similar to the T5 is the standard. The other two are further forward and require a modification kit as the mount ups are different. So it costs a bit more to move the shifter, but the flexibility of locating is worth it.

Forte is the biggest dealer for these transmissions.

http://www.fortesparts.com/index.html