Hi all I have a 95 K1500 with posi rear. I replaced the rear end 2 years ago when the ring gear lost a few teeth. It was a junk yard rear that had 45k on it. Lately (6months or so) I noticed a small lack of power when backing up an incline, very pronounced when backing a trailer up hill. Last week it got to the point where I'd have to put a lot of gas on it to get the engine reved up, then there is a thunk and it goes just fine. It is to the point now that I'm having the issue even on level ground. Any ideas? The thunk definetly sounds like its coming from the rear and not the tranny, but I guess the tranny could be slipping and when it catches it torques the driveshaft enough to cause the rear to thunk when it gets power. I changed the fluid and filter last week, but it didn't seem to make a difference. I haven't checked the fluid in the rear yet. I'll do that tomorrow.