Not sure why this is so hard, I did a lot of racing on Tokyo WTC 600PP with and without Tomahawk X, for all of you that have problems, here are few of my setups that I just came by, most of the cars are basically stock with few additions. All races I did were no stoppers! All races were done in approx 27 minutes, 1st lap usually is 1:35-1:37, then 2nd is approx 1:18-1:20, and then all other laps go approx 1:12-1:16.
BAC Mono - really nice car to drive, keep it in Fuel Map 1 all the time and do a bit of short shift at approx 3/4 of the bar just for more power, has more then enough fuel. Little bit tail happy.
Bugatti Veyron - accelerates out of the corners pretty easy, but it is a chunky boy, really heavy and one can feel it. Fuel Map 6 all the way and short shift at 1/4 of the bar, it is fuel guzzler. Also it does use up tyres quite well.
Ford GT40 - this one I had so much fun with, pretty fast on straight. Can't remember what Fuel Map I used, but I think it was 3, also short shift at 2/3 approx, fuel should be OK. Tyres are pretty good on this one.
KTM X-Bow R - this one was also fun to drive, I think I did this one with Fuel Map 1 also. Tyres are more then good, and also it is a bit tail happy. Short shift at 2/3 of bar, it looses power higher.
Lamborghini Diablo GT - this one has good speed, but is also heavy and a bit tail happy. Fuel Map I think it was on 4 also, and did short shift it at approx 1/2 of the bar. Tyres were OK.
McLaren F1 - really nice one, I have a video of this one also. A bit tail happy, but nothing bad, tyres are also OK. Here is video:
Mercedes-Benz SLR McLaren - this one was a bit harder to drive, since it is really tail happy, but having it in higher gear helps a lot. Tyre wise it was more then good, also Fuel Map on 6 and short shift at approx 1/2 of the bar.
Radical SR3 SL - this one was pretty easy to drive, Fuel Map on 1 all the time, a bit of short shifting at approx 2/3 since it looses power higher, and keep it as much as possible in higher gear since, so if you think you need to drive curve in 3rd, keep it in 4th, has great torque curve. Tyre wise is pretty good as was BAC Mono. This one is slowest on straight (approx 270kph), but it does come back on curvy part of the track.
Have fun!