The TKO is a great trans - been around for a while, and enjoys a good reputation.
It used to be you could get a wider gear ratio spread - mostly meaning a lower first gear - with the high torque rating. But that doesn't appear to be true any longer.
The "Problem" with all the TKO's is that 5th gear is .64. which is a good ratio for highway driving when couple with a 3.55 to 3.75 rear gear. But, 4th is 1.00. It's a big drop from 1.00 to .64 - that equates to something like 1,000 rpm drop. But you're cruising down the highway at a fairly mild 2,400 rpm's (80mph). There are a lot of times on the 2 lane highways I wished I had an intermediate gear.
You can get the .84 5th gear, and you get a much smaller drop in rpm's, easily keeping the engine in the power band as you drive around town and the back roads. But that puts you at around 3,300 rpm's on the highway. IMO, that's too many rpm's for an easy highway cruise.
If I were building again - or I needed a new trans - I would probably get a 6 speed. I would take a serious look at a T-56: 700 ft/lbs of torque, 2.97 1st gear, .74 5th gear, and .50 6th. That would work really well with 3.70 rear gears.
Tremec Transmissions, Technology in Motion
I bet Mike Forte could get you one at a good price - along with all the parts and fasteners you needed, too.