There are a few reasons that can explain the difference you
feel.
First of all, it is the car GC8V itself. At start (0 points), this
car is already equipped with all the mods up till 120k points.
Basically, it's not really a stock car as compared to the other
cars at start. Therefore you would have found it easier using GC8V
than using the other cars, up until 120k points. Oh and you should
know, you can't have part changes for GC8V.
Second of all, it may be that AWD is just your style since you did
play with some other cars and found them not so good. Actually,
it's not that the cars are lousy, it's just your preference/style.
Also I think AWD is also easier to drive than the others.
And finally, it's because subconsciously you memorized part of the
tracks you have played on and so when you play them again, you're
better than when you first played them. Basically you got more
experience so your skills have improved. 
