I've driven several TKO600s, and they all vary -- including those with mods made to them. The one in my ERA shifts like butter; no complaints and no mods to it at all. I've come to the conclusion that the TKO is particularly sensitive to bell housing alignment -- which took the better part of the day on my FE with a Lakewood on there. Either that or the QC on TKOs is like a roulette wheel. I tend to think it's bell housing alignment.
