[KiltedBanshees93GT]

Well, the first thing is to figure out if it is the driveline or alignment/balence or maybe condition of the tires.
You didn't specify what transmission you have, but you should be able to do this with a manual or auto.
Suppose (for instance) that this noise/vibration is happening at 60mph, and 2k rpm.
Just get the car up to 2k rpm in a lower gear, and hold there, if the vibration occurs, its driveline. If it doesent, its either the wheels, tires, alignment or a combo of these.
As to figuring out if there are any underlying problems, If the vibration turns out to be wheels/tires, and there are no other obvious things wrong, I would just change the fluid in the tranny and rear. Look for "off" fluid colors, burnt smell, metal particles, etc. Or take it to a shop to be doubly certain.

Hope it helps,
J