Apparently this is a common issue with chevy trucks. I just got my 99 tahoe back from a very trustworthy mechanic and was told the same thing is wrong with mine. He has a 98 silverado and he said the pitman and idler arm wear out by the time they hit 100-125k miles. If this is something you are interested in doing yourself, here is a great site to get you started.
http://aplsweb.com/Topics/Steering.htm