Squeaky springs

I have a 2007 gmc. I use it daily for towing a construction trailer. The filter head had an o-ring go bad so I had to have it towed. From that day till now it feels like the rear end is loose. It feels like it rolls forward when you stop and rolls backwards when you take off. I have jacked it up, put it on blocks and had someone put it in gear and mash the brake while I looked under it and saw no play anywhere. I have already replaced the spring isolators and it helped a little, but did not stop it. I have sprayed silicone on the eye bolts and bushings, changed the shocks to Bilstien heavy duty shocks. I don't understand how it never did it before it was towed. It was only towed ten miles, and towed from the rear. any help would be greatly appreciated. getting frustrated.

2WD or 4? When you say it was "towed from the rear" do you mean the rear wheels were lifted and the front wheels were in contact with the ground? If it's a 4WD did they have the transfer case in neutral? Did you check the front end for play?

Obviously a bit late for this, but I'd put my truck on a flatbed if it needed to be moved under other power than its own... Automatic transmissions don't like to be turned by anything but the engine.

Do you have an extra fuel tank in the truck bed? I have a 100 gallon tank in my truck bed and it can cause some strange sensations when it is half full and the fuel starts to moving around.
Good luck
John

I tried this type of spring cushion and it really helped removing those squeaky sound.
http://imageshotfrogph.blob.core.win...3446_image.jpg