Somehow I didn't interpret his post same as you did.

Where did he say he had broken exhaust?

And how can an unbalanced drive shaft cause a vibration when the vehicle is not moving?

Am I missing something?

I'm thinking this is a common denominator:

 

That might be so.. that's exhaust rubber mount?

 

Yep. Note proximity of exhaust pipe to crossmember, and what would happen if the trans mount were sagged.

Noggin pokin time!!!!!!

 

Well I looked at it and nothing looks wrong. And that exhaust mount I notched to go around my cross member

 

Lookin' won't tell you if the mounts are sagging, you've got to get a jack under there and see how much movement there is.

Can you explain on this "notched to go around my crossmember" bit? That's not normal unless you have a custom setup or flat-belly pan, etc.

 

When I put new cross member for my long arms I notched it so it has a 1 inch deep radius to go around steel plate.

 

Did you fix this? My 99 is doing this 1800-2400 rpm, a vibration that can be felt through out the jeep, you can actually see the engine vibrating.

 

Sounds like motor mounts.

 

Check exhaust contact with the chassis, trans mount crossmember, rear axle, rear frame.
Check for bad engine mounts.
Check for bad clutch fan, will cause vibrations.
Check for misfire cylinder.