Hello, I know this is an old post but no one ever really came up with an actual fix. I am a professional mechanic and shop owner and I just had an 09 with the exact same issue and all of the forums I checked had a lot of obvious checks but no good repair info and not a single one I found with an actual resolved fix. So the truck I had was an 09 Colorado 5.3 4x4 that would start shaking aggressively after crossing a bridge seem or other large bump and continue until you slowed down to 10 mph or so or put it in 4wd. The actual issue was the left axle stub shaft support bearing was completely shot. when I searched for anything loose that could be getting out of balance I found the inner axle could be moved up and down about 3/8". We replaced the left cv axle and differential left output bearing and it is completely normal again. Evidently it would stay centered even up to 80+ mph but would get knocked of center with a big bump and wobble until either slowed down of loaded with 4wd.