Bouncy Rear-end

After getting my wheels balanced twice, one of them was a road forced, (I have 265/70/17 BF KO2 tires), the back of my truck still feels very "noisy" with "echo bouncing" so to say. If I hit a speed bump, the back of the truck will continue to bounce/wiggle several times after the fact. Any little bump seems like it's an on-going bounce. Sometimes I think it's the balance, sometimes it feels like the suspension is messed up somehow. My previous 4 Tacomas never felt like this. I know the back of the truck is light, but to me, this is quite different compared to my past experiences.

Any thoughts on how to attack this? Might be hard to convince my dealer at this point something is wrong…it's subtle, but driving me nuts!