Its a long read, but it would have saved you a ton of money.

https://blazerforum.com/forum/showthread.php?t=41670


In my honest opinion, your problem lies in your tires/wheels.
Read the thread I posted.

 

Well I had the tires road balanced several times and still the same vibration. Going to replace both hub bearings and see if that will fix the problem!!

 

I returned the Kumho Solus KR21 and got some BF Goodrich Long Trail T/A Tour and the vibration is not has bad. I read that there is a problem that gm knows-Symptom- Vibration that is felt in seat of pants OR a body shake at highway speeds. Recommendation- This condition may occur when EVA readings show the tires at 12-14 Hz, OR 60 MPH, and 0.07 Gs. This condition may develop or worsen on rough roads. This vibration is NOT torque sensitive and Can't be felt in steering wheel/column. This vibration is considered a normal characteristic for these vehicles and no repair attempts should be made. This diagnostic approach was developed for the VIN you entered and shouldn't be automatically used for other vehicles with similar symptoms. (end) They are admitting the problem exists, but saying it's normal, and there isn't a repair that will remedy it. They may eventually update a part (discover a design flaw) or develop a repair but at this time choose to say it's normal. Go over [#PI01273B - (09/15/2003)] with anyone else that drives your blazer and the service technician at goodwrench to determine if the symptoms match the bulletin. It is more of a oscillation that is intermittent in intensity especially when accelerating. I will replace the hub bearings and install reman cv half shaft(was leaking grease) tomorrow .

 

Replaced the front hub bearing and installed cv half-shaft. Replaced the rear bearing-had tires road force balanced again and I still have the vibration 65-75mph. This is a 1998 4x4. I've replaced everything that turns in the front and rear. Tried 4 set of different tires-no difference. Would really like some help !!!!!

 

could be a drive shaft issue. I would try swapping a drive shaft with one from a truck with no vibrations. or your local machine shop may be able to balance yours.

 

I have the same thing. I thought most Blazers came with a back massager option.

 

Haha. I have it too. Keeps me from speeding lol

 

Had the driveshaft balanced and new u-joints installed.

 

I know you've tried a new set of tires, but check for out of round tires. I've seen this a lot, you can balance one perfect on the balance machine, but if it's out of round it doesnt matter, it will vibrate at a certain speed. I've had this problem on a corvette with new tires, most dealerships, tire shops dont ever think new tires would have this problem. I took it to a local "good old boy" big truck/diesel alignment wheel shop. Jack up the rear of your vehicle and support it well. Start engine and put in drive, look at your tires while it idles and the tires turn. I only had to jack mine up about 2-3 inches from the concrete and one of my tires was really obvious it was out of round. Replaced that tire and it ran smooth. You can do the front with just spinning by hand. The out of round tire will be very noticeable. Back in the 50-60's they used to spin the old bias ply tires on a machine while another machine actually ground down the tire as it spun to make it perfectly round....

 

i had a truck into the shop the other day, you should try the axle bearings in the front diff,and check the pinion bearing as both of were f*** up and i fixed them and the problem went away!!