I'm making a solid bet that you've added the biggest turbo you can, and it'll accelerate up to a point, then slows down, speeds up, slows down?
IT's hitting the REV limiter. You need to adjust the transmission.
GTPlanet is not here to spoon feed young children. We also don't suffer fools easily. You need to take 15 minutes and read a few posts, before posting again.
It takes me less than 15 seconds to ban someone, and your approaching the first of the weekend.
AO