I'm having a BAD vibration around 1000 rpm. The vibration shakes the whole car. You can have it idling and visually watch the exhaust just shake. It's even worse at 50 mph. The whole car shakes. Put it in neutral at speed, no vibration, put it back into gear, vibration returns.
Motor mounts?
Tranny Mounts?

 

Driveshaft

 

Before it started this. I would sometimes here a loud cracking noise. Drive shaft? Even if I can watch the motor and exhaust shake in park?

 

I'm just thinking becasue most driveshaft vibrations happen when it's in gear. And the DS vibrations are pretty strong. Usually they'll stop when in neutral. Since the DS is not engaged. But when you say the car is in park and it's shaking the only thing still spinning is the Flywheel. So that my lead to something going on in the clutch area.

 

Actually, anytime the car is moving, the driveshaft is moving, putting the car in neutral will have no effect on an out of balance driveshaft. The car in neutral only means that the gears in the tranny are not engaged, however the rest of the drivetrain is still moving. The clutch does not engage the driveshaft, it engages the trans input shaft, which engages the gear, turning the output shaft, to driveshaft, to rear end, etc. So if the vibration goes away with the clutch pressed, it is not a DS problem, it is a clutch/pilot bearing/tranny problem.

 

I'd check the motor and tranny mounts if you get a lot of shaking in idle. From what I've read and from my own experience, driveshaft issues usually begin at a certain speed and up; most commonly around 75-80mph+ My driveshaft vibe started at 82mph and got progressively worse; car shook from what felt like was the radio/centerconsole/shifter area

if that's any help Brian