2006 SRT 10 Quad Cab rear end clunk

This is automatic with 32K miles. Only at low speeds and rpm's I'm getting a clunk noise after a shift which I believe is coming from the rear end. It will also do it at low rpms shifting into second. It doesn't happen when she runs cold but only after 5 miles of driving. When I accelerate up to 30ish mph, and take my foot off the gas pedal I hear the same clunk noise. When I floor it or give it a minimum of 40% throttle I never hear it. The tranny shifts perfectly with no problems whatsoever. I have only had the truck for about a 2 years and put 5K miles on it. I brought it to a reputable Dodge dealer. I met the mechanic, he was excited to work on it. I took him for a drive and he heard the clunking. He wanted to open the rear end, take a look at it and change the fluid. He found nothing wrong and a clean magnet drain plug. He did notice my springs were a little loose, they needed about a half turn to tighten. He also looked at the tranny and bands, U joints etc. Nothing wrong at all. This 20yr Dodge mechanic said he has never worked on an Srt10 but has worked on the same V10 and the same transmission. He also stated Dodge, especially the older ones are known for the clunk aka driveshaft slack etc. He hooked up the computer to it, diagnosed the tranny etc. Does anyone have any idea what this is? I'm trying to avoid bringing it to the best transmission shop in my area. They charge $200 just to say hi. Any idea what this problem might be?