I own a TKO long time ago. Hard to shift so I bought a high dollar shifter. Helped a little. I did not like the 3.27 first gear. Sold it and bought a TKO 600 with a 2.97 1st gear. Lot better but still hard to shift. Put about 30,000 miles on it before I pulled it and put in the Liberty Gears street upgrade. WOW what a big difference. Smooth as a wore out T-5. Could not miss a gear.
I have driven a couple of 3550s. One in a 530 hp 408 for a total of a couple of thousands of miles. Never spun the rear tires. I know, that was hard.
The other Cobra with the 3550 has a 487 K.C. 620 hp side oiler. I've put a few thousand miles on it through the years and I've spun the tires a few times. Both 3550 are smooth shifting, easy to drive trannies. I would highly recommend the 3550, out of the box, over the other Tremecs that I have driven.
Now the 600 with the upgrade has to be the best.
Dwight