No idea what it could be.

[FuriousGeorge]

Hello, I'm new to the forum and I had a question regarding my 2005 GMC Sierra 1500 Z71. I've taken my truck to a couple shops around town and they either "fix" it and charge me, or they just say it's normal. Let me explain the symptoms... the truck acts as if there's 2 separate parts to it, the frame, and the body. When I accelerate from a complete stop, I hear a noise I can only describe as a "shifting" noise, almost as if the frame starts moving and then the body of the truck shifts after it. The same thing happens when I stop. The frame stops and then it sounds and also feels like the body wants to keep going but then has to stop because of the frame. I've gone onto youtube and looked up all kinds of noises and I can't seem to find what the problem is. I don't believe it's the U-joints, it doesn't make any noise and they appear to be very snug. One mechanic told me it was the leaf springs shifting on top of each other, he put a lot of grease in between each spring but it didn't seem to make any difference at all. When I bought the truck, I bought it from a small dealership that said they had to replace the body mounts when they took it from the previous owner. This "shifting" noise is exponentially worse when I'm towing. My biggest fear is that I'm going to be driving one day and when I accelerate, or stop, something (whatever is shifting) is going to snap and I'm gonna be left with a huge mess. Please give me any information you can. Or maybe have a suggestion on who I need to send my truck to to have a real idea of what's going on. I was going to send it to a tranny shop but they charge a lot to even look at it. Thanks in advance,

-George