[MuskyHunter]

I think I know what you are talking about. I drove a LWB with my buddy when he was looking for a new truck. Since the dealer only had a LWB in the lot to test drive, we gave her a run. I did notice a difference in the rear of the truck compared to my SWB KC. What it feels like is the higher spring rates in the rear or slight flexing of the frame. It is a quick, quiver like sensation.

Tires can certainly play a roll and have been very pleased with my new tires. If you have the Continental tires, and if they are anything like the Conti's on my wifes Altima, they are a harsh, not very compliant tire indeed. On the cheap, try running your front tires at 37 psi and the rear at 35 psi. This will induce a small amount of oversteer and works out quite well. If the dealer is cooperative, maybe they would be willing to swap out a set of rear wheels from another truck that has h a different tire, such as the SRA's. Approach this request as part of troubleshooting the problem.