I bought my 97 burb new and it has done the same thing from about 14K miles on. The dealer could not find anything and thought I was too critical by reminding me "it's a truck not a sports car". What I did find was that the shaft itself is loose where it goes in to the steering box. You can move it about a quarter of an inch up and down or side to side. The dealer told me this was normal too!
I now have 119K miles on it and the whole suspension is still tight, and I've only had to replace the idler arm every 35K miles. But I still have the play and clunck in the steering. I might try replacing the steering box and/or shaft, but I think that might be big bucks$. After a recent inspection, the looseness is coming from either inside the box or where the shaft connects to it.
Any ideas? Can the box be adjusted or is there a mounting flange or something that can be replaced?
THANKS!