When I saw the title I wanted to say to check the tire for rocks or nails, but since you bought new tires I guess that's not it.
I had the same problem on my 1999 Suburban, but it ended up being sticking brake calipers coupled with warped rotors on the aftermarket disc brake system that I have. I just rebuilt the calipers and replaced the rotors and it went away. If you have drum brakes on the back that could cause the same thing if they are binding up. Even though you had the brakes checked already you may just want to get a second opinion to make sure.
Another possibility is that your rear axle bearings are going bad. At 150K if you've never had them replaced it may be time.
Wednesday, September 12th, 2007 AT 3:56 PM