> try to change the vinyls in the 08 Shelby GT 500KR
As mentioned in my prior post, the GT 500KR vinyls are part of a "stock graphics" package and can't be changed. You need to delete the "stock package" and then add the vinyls back. I think the chicane vinyls include the stripes which you can move, resize, and color to match the "stock graphics" vinyls.
> Porches and Mazda are over powered compared to American cars ... balance issues.
Most racing games have dominant cars overall and/or dominant cars for each class / tier. Which cars are chosen to be dominant don't reflect reality, such as choosing the Toyota Corolla to be the dominant race car in Underground 2.
For UC, the dominant tier 4 car is the Elise. For tier 3 - Nissan GTR, closely followed by Audi TT, Dodge Challenger, Lotus Elise, and Mazda RX7. The Challenger has more power but less handling, so unless you know the tracks (you need to brake sooner), it's more difficult to drive, but I recall players using the Challenger online in multi-player races. For tier 2 - Lamborghini Gallardo or Porsche GT2. For tier 1 - CCX if you have collector's edition, otherwise the Zonda. The McLaren F1 is the easiest tier 1 car to drive if using an analog controller, since the steering is so sensitive in the tier 1 cars. For tier 2 and 1, the downforce is a key issue, as many of the cars go airborne over bumps, causing them to crash in turns. Using nitrous unrealistically increases downforce, so it's often used in turns, but it's not enough to keep most of the faster tier 1 cars from going airborne. From the Challenger Series, the Dominator Z06 has great acceleration and top speed, but it's lack of downforce makes it useless for racing.
> The pursuit break around the court house is important.
If that's the one I mentioned in Palm Harbor, it's the only one I'm aware of, and someone at EA just forgot to put the pipes there. Once you know it's not there, it's not that much of an issue as there are other pursuit breakers in the area, and the more difficult pursuits in career mode are in Sunset Hills and Port Crescent. If just trying to evade with the helicopter present, I use the highway that goes through Palm Harbor, use speed breaker and u-turn just before the bridge to lose the helicopter, then head west and take the pair of jumps to the isolated bit of road.