Look into intermediate shaft. I don't no the exact years it effects but I think it effects 99's. There is a lube kit from GM consisting of a plastic siring and rubber cork for $10 - $20 dollars. Take the intermediate shaft out and pull it apart(expand it), put the grease from siring down the tube. Cork the end and ca-lapse it, grease will shot out the splines. I recommend filling the tube completely with grease so that you don't have to do it again for a couple of years. Brand new ones have the same problem, but they have fresh grease.
