Yeah it was mainly the power to the motors setting. The reason it was shaking was because the motors weren't receiving enough power. and once I bumped the power up a bit the shaking stopped.
I did have to adjust the PIDS at a later date to get it perfect though.
I think I increased the power by around 10 points. It was on 50, I made it 60 or 65.
As of the PID, thats hard. Each situation is different. You asking 'in what way did you have to alter the PIDs' is like asking 'in what way did you turn the steering wheel to get around the track'. It's just hard to answer.. You'll have to do some searching on PID adjusting and try to learn.
The PID and the power are all related to each other.. Sort of. Once you adjust one setting you have to do the other.