2007 Chrysler Aspen / loud shaking
 

My Chrysler Aspen started shaking at certain speeds but especially on freeway. It stops when I apply the brakes or acclelerate. It also shakes at low speeds. I had 4 new tires put on around 5 mo. ago. I took it to a local mechanic but, of course, the shaking stopped. He ran a diagnostic test and nothing was wrong. I am on disability with a limited income and every time I take my vehicle in to the shop they find a ton of problems and I leave feeling like I have been totally taken advantage of (I am clueless when it comes to automobiles). I just wanted to research the problem before spending a ton of money...Any ideas?

were the tires balanced when they were installed?