Ran 3 autox this weekend with the new Kumho's, found through trail and error that low pressure works better. Tried 41 and 31 at first, reduced to 34 and 33 and it seemed to work real well. Another guy with a 350 tried the same thing with the same results, and he had R hoosiers. He had been up around 46 in the front.
Our air temp over the weekend was around 90 degrees, we found on the other days our times where getting worse as it got hotter out. So in desperation found the answer was reducing tire pressures. Give it a try and see what you think, hope it helps.
John

 

I ran my Kumho Ecsta's on a 70 degree day on track wheels 225/40 fronts 265/35 rears 40psi front 37 in the rear. Seemed to handle OK but I have nothing to base it against. Were you running 17's or 18's??

 

We where both on 18's, he had 245 all the way around and I had the 265-225 setup. One guy that knows what he is talking about thought that it was to big of a diferential with the 265 and 225, we have also been trying one turn on each side of toe out up front. Car still seems to run on the outer edge up front all the time, wish we could get some neg chamber somehow.
Another thought is the front stab bar is not stiff enough, and we where speculating about shocks. The other 2 guys I run with are both former Nat'l champs multiple times, so it is interesting to get the feedback from them.
Thrid Z guy found that Mustang rims will bolt right on and have the same offsets for an enthusiest(sp) model, won't work on the track models, he is running my old cobra rims and 255/35-17 all the way around, so all those guys can save some big bucks
John