Get a fitting with the T400 heads and try them with multiple shafts. I assume you did this already since the AMT black isnt the off the shelf shaft for the t400. The C taper lite is a lighter shaft and in theory would have an easier left tendency. Work with a fitter and see what is causing the left tendency - my guess is it is not the shaft. That being said it will give you a chance to try other options and see if something works better.

Incrimentally, yes. The main thing to remember with iron shafts is that raw frequency is not really something to be a hardliner on. What you are feeling is the different bend profile of the KBS. Even if the two frequency out the same, which they shouldn't be too far off of, given they are both Regular flex, the bend profile and how you load the shaft is paramount.

Basically, if you hit a different shaft well, there is a reason. Be results driven. If you see noticeable results then go for them.

When I was fitted for my T300s, we tried a number of different shafts until we got the right one for me. We ended up with the AMT Red R300. I hit Project X, KBS, and others because I wanted what best I could get and price was not an object. With my 7 iron, was dead on the flag at 165 yards. Was 73 at the time of the fitting and felt pretty good. My fitter (who has been with Titleist for over 25 years, a Product Specialist and one of their best fitters) allowed the time needed to get the correct combination of shaft and head to attain the best performance for me. I am a proponent for getting with a qualified certified fitter and will continue to do so anytime I purchase new equipment. As we age, our game changes, and we need to adapt to those swing changes. With respect.

Thanks for your reply

Completely different shafts- the KBS are a constant weight shaft and likely has a greater frequency increase as you go from the 6 iron to the 9 iron which would provide some protection from going left- its bend profile may be a better fit for you. As SNachilly states "be results driven". Also with no industry standards don't assume any match in frequency based on the flex designation on the shaft.

Thanks