ok so im new , my car recently started shaking its bone stock. it was running right till on my way home a got paired up with a 240sx, aveo, and civic all trying to race so me being 16 slammed on it i ran it hard(about 115-130mph) for about 5 min. had to exit the highway so i pulled off and noticed my car was shaking. i read on other threads and they said harmonic balancer so i changed it thought it was a little better so i took it about 1hr trip and then back. all the while still slightly shaking next day drive it about 5 miles when all of a sudden it started shaking like crazy!! as if i was in an earthquake. so i went and changed the harmonic balancer again. making it twice it still shakes horribly. it is worse in lower rpms then again hitting about 2000 rpms. its driving me nuts i dont know what it is. by the way its a 91 mustang gt c4 auto with overdrive about 110k miles. someone please help me!!