Hey guys I have a 05 2500 HD with the LLY Duramax Allison 1000 transmission two wheel drive extended cab 8 foot bed the problem I've been having is when I come to a complete stop and start again there is a large thud and almost feels like the rear end sits down a little bit like something is Shifting front back I installed an entire front end by Moog so i dont belive its in the front. I have Monroe shocks front and rear . weird thing is is when I have a load ON the truck it does not do it . I've done research and they said something about the slide yoke needing a goid greasing but it feels like more than the yoke sliding. when I got the truck it was wrecked in the front but I've restored it, now could it possibly be slide yoke and also a transmission mount and how would I check for that let me know what you guys think thank you

 

It's fairly easy to grease the slip yoke so I would do that to eliminate it as a possibility. it should be done anyway.

 

Paul,

URGENT!

I have a 1995 Chevrolet Suburban that I have had for years. And use like a truck to haul things in the back since all the seats fold down. And taking my dog to the lake!

Back to your Question.
Recently I was having the same thing happening to me. I finally took it to a local mechanic. You need to get your truck into a mechanic right away.
My entire Rear End including my Differential was nearly ready to fall out from under the truck!
Both large U-Bolts that holds the rear axel housing under the truck had completely rusted out. And at the time the only things that was holding the entire rear end to the truck were two small links! And they were stressed to the point of almost breaking. I was very lucky I went and had it checked. Not to mention the damage that would have occurred if the entire rear end would have fell out from under the truck.

RCC

 

It might be the backlash in the rear diff. Mine does something similar at times but not always. Put it in drive with the brakes on and give it a bit of gas to load up the rear end. Then let off and put it in reverse to see if it clunks. Do the same from reverse to drive. It's helpful if you can have somebody look at the driveshaft while doing this to watch for movement.