This noise has come and gone, but now it's back - a thunk noise when I turn right and when I turn left it thunks back. It only happens when I turn right first, not when I turn left first. It feels like it's comming from the middle of the truck.

I've had it into Chevy a couple of times for this and each time they changed the intermediate steering shaft.

Has anyone had this issue to deal with? If so, what was the outcome?

First you can check if it's the intermediate steering shaft, open the hood and grab the U-joint that connects the steering shaft to the rack-N-Pinion steering. Move it up and down and you will feel the clunk in the steering column, that will tell you if this is your problem.

Other items to check, the sway bar/bushings, mounting bushing for the torsion bar cross member if worn, the ball joints.

Sorry I can't be more help to you. By the way, the true fix to that intermediate steering shaft is here, part # 937; http://www.borgeson.com/TruckProductChevy.htm

Thanks for the response.

Chevy says that the last intermediate steering shaft was "the latest and greatest".

Now it seems that the thunking has dissappeared. I've looked underneath the truck, tried to move the suspension components, and nothing. Everything seems intact. This seems to come and go.

Gm originally was replacing the interm-shaft. Then switched to packing the shaft and now back to replacing it. Minor fix but crazy how you are not having the problem anymore.

As of yesteday afternoon the thunking has returned
...and of course the truck is offically out of warranty as of last Wednesday - 100,000 miles.

Maybe you can convince them into getting it under warranty. The last dealer I worked at was good about helping people out like in your situation.

Since you have documented the problem before the waranty is expired, they have to fix it under the waranty. Besides, if it is the shaft, it should have its own waranty; howeverm if it is the shaft, I beliave GM does not have a solution for it. I know lots of people said the thunk is back even with the latest shaft.

So, you may want to give a try to the shaft Quadrant is advising..

My truck has the problem again and after 5 years no longer under warranty so I think I am going to go with the replacement shaft and get the problem over with.
http://www.borgeson.com/TRUCKS/CHEVY.html

is the updated link for anyone else looking for it. thanks for the find Quadrant