My 2008 Chevrolet 1/2 ton 4 wheel drive recently developed "clunk" when going from drive to reverse. Note - front wheels disengaged. The "clunk" to me meant play and I figured it was in the rear driveshaft universal joints. This past weekend I crawled underneath with the transmission in neutral and could not identify any slop in the front or rear driveshaft universal joints. While twisting on the driveshaft I noticed that there is quite a bit of play in the differential. The driveshaft might rotate an 1/2 to 3/4 inch. I have never had a differential problem in a pickup. Are these pickups prone to rear end problems? Is that amount of play/rotation of the driveshaft too much? Seems like I have developed a vibration or rumble at highway speeds. Let up on the gas pedal (coast) and the vibration/rumble goes away. The vibration resembles a very low tire. Can the rearend be rebuilt or do people just put one in from a auto parts yard. Any ideas appreciated. Thanks.