I have a 2008 sierra c1500 5.3 and having problems. When i come to a stop it feels like the drive shaft comes forward and hits,and when i take off it feels if it goes back and hits.

 

slip yoke. pull it down and grease it, there is a TSB for it.

 

its really common and gm is aware of it and says it normal. though i would have thought they'd fixed this on the nnbs. but you should be able to grease the yoke going into the trans and should help for 15000-20000 miles.