Did you go all out on the TT??? I've ridden in one locally, but nothing compares IME to Underground Racing's TT vipers and lambos here in Charlotte--those care jump north of 200 in about 18-20 seconds. It's just not right to trap 168mph in a 1/4 and still pass emissions along with keeping the AC etc.
I use to have a nice Is300 with a 2jzgte block in it and a big single turbo, but tires with an ounce of traction could not be fitted without an ugly wide body kit. Try putting down about 675rwp down to 245 35 18s!!
I bet there are not a lot of vette guys that would know the Is300 has a better drag coeffecient than a C5!!!