Does it idle really low when first started? That can cause the shaking you are describing.
Just the first thing that came to mind because I had a old plow truck that did the same thing, I never bothered to figure out what caused it to idle low at start up since it was a plow truck and wasnt worth the effort.
"Time you enjoy wasting, was not wasted"- John Lennon
"The Jeep is a manly device. And a womanly device. An American device. It’s a fitting instrument to transport the free people of a free nation with the respect to which we are entitled and the dignity that we deserve. Okay, we’re a little crazy to have a Jeep for a daily driver. But if we go off our meds, we might wind up in a Prius"-P.J.O'rourke