Vibrations!! Please Help!!

I have a '99 Silverado Ext. Cab with 5.3L with 120K miles. My truck is shaking!!

At about 90K miles, I noticed that my truck had a "shimmy" when I accelerated from 15-35MPH. Now the "shimmy" is more like a shake and the truck shakes pretty good whether I am accelerating, coasting, or braking in this speed range.

Does anyone have any idea what could be causing this?? It's driving me crazy and I'd like to figure it out instead of taking it in to have it fixed.

What are some common sources for a truck to shake??

Thanks In Advance,
Steve

Check your lug nuts and motor mounts

Also check your ball joints, and all tie rod ends. It wouldn't hurt to check your idler arm either

Just a shot in the dark and mayby a thought. I wonder if your front rotor bearings are bad or if the bolt that holds the rotor on is lose. Im not sure if this would cause your problems but its something else to check.

Also I wonder if your transmission is not downshifting and is enguageing the torque converter lock. I think it would be something like trying to take off in 4 th gear with a manual transmission, (it makes the whole truck shake until up to speed). Never seen this happen, but like I said, its just a thought