One of our readers, Matthew Davis, came up with a possible solution for the Tundra's bed bounce.
Basically, he took a piece of foam rubber and placed it between the back half of the spare tire and the frame. Then he tightened the spare back into place and effectively the spare became a damper.
Here's a basic picture:
You can see that it's not much foam in their, but he says it made a big difference on his truck.
The full explanation on more photos are on TundraHeadquarters.com
Possible Tundra Bed Bounce Cure Found | tundraheadquarters.com
Hope that helps.