So I am level 28 A-Spec. My fastest car is the Corvette RM that I race in the American Car series. I have 5.5 million in credit. What vehicles should I be looking for for the next few levels in my career?

a car that is almost considered cheating, should be your next choice: chaparral 2j...that should be banned lol

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1997 Eagle Talon TSI

In fact, it hasn't been allowed to race online with us yet!! Damn thing is unstoppable. Have to watch the used dealers for them. The easiest way to make money in the game, with out running B spec cheats, is doing the seasonal events. You'll be able to rack up enough money to buy whatever you want in short time. Just buy the cars that you would like to drive and mess around!

Ok sounds good. I'll just keep making money and buying whatever cars I need. Now a question for the guys I race online with. What do I need to work on to improve my lap times?

I always tried to race with that mentality as well, "how do I get faster!!" But, I'm slowly coming to realize that if you focus on being consistent and not wrecking, the lap times will come. When I first started racing with these guys in late December, I was able to run a similar time, but would always finish a lap or two down because I wasn't consistent, now I am wrecking less and finishing better.

Jason hit the nail on the head focus on driving smooth and consistent. That will net you the biggest gains.
When I'm qualifying I do 10/10ths or even sometimes 11/10ths.... and I crash.
During the race I never do more than 9/10ths, I'm always just that little bit cautious. Sure sometimes mistakes happen, but the trick is to minimize those mistakes.

Since the new tire it's super important not to squeal your tires, If you hear your tires squealing you're just wasting time and tires. This will also help you eek an extra lap or two out of a set. Less time in the pits equals more track time. Now since one of the last updates the tire squealing sound has been really reduced in volume, so you really need to listen and pay attention for it.

Now, once you're fighting for tenths of a second try the following (IN PRACTICE):
Never try any of these this under race conditions until you are 110% comfortable with them.

-Turn the driving line OFF
-ABS 1
-TC 0 (Even with a Traction Control setting of 1 or 2 it will slow your car down, especially on exiting corners)
-Setup (Now this is personal preference, but get the car setup so that you have full confidence in it)

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"The future is already here — it's just not very evenly distributed."-William Gibson
1989 Van Diemen - Formula 2000 Continental