My jeep grand cherokee tsi shakes too. It would shake whenever it felt like it, up hill down hill, turning, hitting the gas hitting the brake. My brother followed me one day and said it looked like the front end was about to fall off. I had a friend of mine drive it and he said it felt like something loose in the front end. we checked and all he found was the ball joints have a little play in them. i can't change it until the weekend, but i'll post if it works.
Shaking... can drive it for a bit then it starts to shake uncontrollably. Have cleaned injectors, replaced spark plugs, fixed vapor leak. What else can it be!!!!!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic