Hiway speed vibration

My '04 TB has 8500 miles since new 8/04. Have always had a vibration at hiway speeds. Dealer first rebalaced all four tires without much success. They drove it today and seem to think it's a "driveline" issue. I don't know more than that now, but will keep all posted. Has anyone else heard of this condition?

I've heard of the driveshafts being out of balance or warped slightly. It definitely is not normal cause ours is smooth as silk. Hopefully they figure it out.

The service tech did feel the same vibration I have. They changed tires with another TB with the same results. LATTOF CHEVROLET of ARLINGTON HEIGHTS ILLINOIS, then just put 25#'s of pressure in each tire and sent me on my way. That is probably an unsafe tire pressure, but they let me drive away to pick up my family. I have a call into Chevrolet customer service now and will keep all posted.

last summer I found a post on here about this, it had all the info about a service bullitin to change the springs. I took it to the dealer showed to them and they did it and my vibration I was feeling at around 55-60 mph was gone. I can't seem to find the posting now ?

See Post 271 On Page Two

I cannot find the post you are speaking of. Can you please add something to it so it will be brought to the front of the forum?
Go to top of page and click page 2, there are 392 postings on trailblazer
look at post # 355.
02-03-09-002A; replaces 02-03-09-002; Intermittent Boom, Rumbling Noise and/or Disturbance Heard in Passenger Compartment While Driving at Highway Speeds (Replace Rear Coil Springs); 2002-03 Chevrolet TrailBlazer, GMC Envoy with Rear Coil Springs
service.gm.com/gmtechlink/ images/issues/nov02/TLNov02e.html

Well... I will drive it for a week or two and see how it goes. The problem may have been "flat spots" on the tires due to non movement at the dealer I purchased it from. This condition is improving not gone.

Mine has vibrated at 63 to 66 mph. Tried 3 times before 35k and they wanted me to replace the tires. Didn't work and now have over 35k and will have to deal with it like this.