I've got a clunking noise when decelerating in the lower three gears. As soon as i pick up the throttle a little bit the noise goes away. The noise sounds like its coming from the trans but i'm not sure. I put the back up on jack stands and ran it that way and it didn't want to make the noise. Anyone have any ideas?

 

Could be your down pipe hitting the frame due to loose or worn motor mounts. Just a thought.

 

Transfer case?

 

A "D" truck has no trasfer case.

U-Joint?

 

Idk the U-joints aren't that old but that doesn't mean anything.

 

mine does that stuff to when your floored and let off hard

 

If you still have the back of the truck up on stands put it in neutral and shake the driveline & the yoke on back of the tranny/rearend. Does your truck have a carrier bearing? Check the bearing and the rubber around the carrier bearing. If that doesn't turn up anything pull the cover on the differential and inspect it. Good luck hope it's nothing bad.

 

What clutch do you run? It seems like my SB likes to be a little aggresive on down shifts sometimes, pending on the weather. Also I've had my exhaust bind and hit the frame rail. check motor mounts.

 

I just put a new sachs 13" in it not all that long ago. Took away the banging noise i used to get when letting out the clutch and now i have just recently noticed this clunking noise.

 

Check the cross pin in the rear end. I have had 2 that pounded on decel and the pin had stretched the carrier and was hitting the pinion. I lost 1 rear completly and saved the other one.