when i hit 4500rpm my motor stutter and then it cont only at 4500( between 4000 and 5000. i was thinking i need to replace the clutch.

i need help with this problem

Does it do this on every gear?!?!

just in 5th gear. it will start climbing and then pause then it climbing

ack.. sorry bro not sure about that one :( :(

you have to describe in more detail. your question is too broad. does the whole car shake? does the rev's rise real quick but the car isn't acelerating? does it feel like there is a fuel cut off? what is wrong with the car?

it only happens in 5th gear in any other gear its fine. it kind of like when your in 1st a you dont give it gas bust just for a sec

You have hit the speed limiter. Since it only happens in fifth gear, your car is travelling pretty fast at 4500rpm. The shaking is because your fuel cutoff or rpm limiter is kicking in, causing surges in power.

is that easily fixable?

its not broke. its the factory limiter on the car. there are ways to bypass it. but i'm not exactly sure how.

edit: it only happens at around 120mph right?

probably at 118mph, which is the speed rating for S-rated tires, which most cars are equipped with. The next step up is 130mph for H-rated tires.