hi.
ok...im gonna tell you what happened...
i just washed up my 88 gta 5.0l 5 speed....runnign mint clean...i was on my way home and a porche carrera s new one got all up in my grill and i raced him 2 times. on the way home.

this car was mint mint mint 140 no vib at all...

i raced him the 2nd time....im losing pretty bad 2 cars.....and its pulling pulling 3rd....i slamed 4th...pulling up to about 4000rpms....im going like 150kmh 170kmsh ish...and it all of the sudden starred vibrating and shaking really bad...so i slowed down it kinda went away...
i drove it around the block and it doesnt seem to shake or vibr untill 50- 60mph or so....but it never shook before...

any ideas????
plssss??