1997 quest shaking

I have a 1997 nissan quest, it just started shaking today when I get up to almost 50, not sure. Yesteday, I had brake caliper , brake pads, brake roter , they replaced front brake pads, and roters,left front caliper, then clean and adjusted rear brakes, , I drove from shop to office 3 miles, then home 5 miles, then back to work 3 miles, then to get gas. 6 miles, then on the way back home after 1 mile started to shake and shake. now i know when you get bad gas your car just stops , so any idea what this is related to?

I have a 1997 nissan quest, it just started shaking today when I get up to almost 50, not sure. Yesteday, I had brake caliper , brake pads, brake roter , they replaced front brake pads, and roters,left front caliper, then clean and adjusted rear brakes, , I drove from shop to office 3 miles, then home 5 miles, then back to work 3 miles, then to get gas. 6 miles, then on the way back home after 1 mile started to shake and shake. now i know when you get bad gas your car just stops , so any idea what this is related to?
hi, i kinda had he same issue, see my posfrom today:
http://www.automotiveforums.com/vbulletin/showthread.php?p=3641756