I have a 1994 Camaro z28, when im driving on the highway im getting a vibration in the rear of the car when i exceed 75 miles per hour. i just took the car to the shop and they said the exhuast pipe is sitting on the crossmember going over the rear axel. would that make the car vibrate like that and why wouldnt it do it when i drive slower???also when im driving and i really slam on the gas the rpms go up but the wheels dont spin, meaning i could be cruising along at 55 miles per hour and when i floor it the car just doesnt go anywhere but the engine revs up, what could be the problem i appreciate all your help thanks.

I would guess your first problem is an out of balance tire or driveshaft. Your second problem sounds like your transmission is slipping. Take a look at the transmission fluid. It is dark and smells slighty burnt? It should be bright red.

the car is manual i forgot to mention that so it would be the gear oil and would that still do the same thing???i appreciate your response thanks

If it is a manual and rpms go up and mph stays the same, then clutch is slipping.
Need a new clutch system and maybe a flywheel resurfaced if it isn't overheated too bad.

thanks i appreciate it. thats what i thought it was but wasnt sure. thanks again.