Lots of posts with pictures on the truck forum websites showing the locations of the grease points. The three in the middle are very difficult to reach and I bought a right angle adapter and a pistol grease gun to make the job as easy as possible.
GM recommends adding grease every 3,000 miles with these trucks so I do it myself as my oil change intervals are very 7500 miles and I don't trust the oil change guys to go the job properly even then.