I've got a 97 4dr blaze, 4.3 4x4. This started happening when the extremely cold temps started coming around. I'll go out n' start her up to let it warm up before work, starts up like a champ may I say. So I go get in my warm blaze, and I put it in reverse to back out of the drive, and it takes maybe 1/2 to a full second to engage in gear(cold weather I believe) and the rear diff(90% sure it's the diff anyway) will 'clunk' into gear. It's just like a loose motorcycle chain when you dump the clutch. It will pick up the slack and 'jerk' because of the looseness. Same thing with my blaze, but no chain, lol. It just clunks. My dad's 96 silverado does it too, so I'm assuming it's just the cold weather and the fact it's 12 years old and parts are warn? Thanks!

 

I would recommend checking the rear driveshaft universal joint that clamps to the input yoke of the differential. When it wears out, it sounds just like what you've described. I had a '98 Jimmy that had gotten so bad it sounded like the differential itself was toast, but it turned out to be just the u-joint. Jack the rear of the truck up, and try to turn the driveshaft back & forth. If the u-joint's gone, there will be slack & looseness between the back end of the driveshaft and the input yoke - it should be nice & tight (no slop).

 

I had this same problem and thought the differential was screwed...but i was wrong while driving on the highway the universial snaped and down went the diveshaft. I recomend doing something about it soon as possible.