Rough idle, vibration, shimmy @ 50-65 mph on a 94

When traveling at high speeds, my 94 blazer idles rough, vibrates, or shimmys. I don't know what is causing it. The computer is clear. Just replaced the egr valve, spark plugs, and fuel filter, and it still does it. The wheel bearings were checked and nothing appeared to be wrong with them. I jacked it up all four wheels off the ground and brought it up to high speeds. No vibration from any speed. There is no vibration at any speed below 50 when traveling on the road. When it starts to vibrate, i will throw it into neutral and the vibration will cease for the most part. Any helpful hints or advise on what to check would be exremely helpful. Thanks in advance!

Check the tires if they are worn, say a year of driving. Chances are that is the problem. That is when I know it is time to replace mine when I get vibration.

Nope, they are brand new tires. They still have the blue on the letters. This is really starting to get me upset, not mad, but upset.

could be your driveshaft not balanced or a u-joint amongst other things

try cheking the fuel injection unit (or the cpi as it is also know as )mechanism under the plenum it seems to go bad frequently and cause all the simptoms you have discribed email me if you need further information @ [email protected]

Iam haveing this exact same probleam on my 95 jimmy. Did you ever figure out what was causeing your probleam. If so let me know please.

Listen to Vinnie.
It's a bad U-joint on the driveshaft.