Gen 2 bed sags with load

Hi All
I have an 08 TRD Prerunner, 177k miles. Went of over a speed bump with 4 kids and buddy in the bed en route to a park. I go over those long speed bumps and as the rear wheels come over it feels like the bed/rear of the truck never comes back up. I slow down for the next one an it does it again, but, not as bad. Almost like it is bottoming out. Additionally, I do get some sag when I hitch up to my 16' skiff.
Is this normal? 4 kids maybe 120 pounds each (480 pounds) and one adult around 300 pounds. New Blisteins 5100 installed last year front & back. Any help would be appreciated.

 

leafs are most likely shot with that mileage, sounds like its time for new leafs or maybe some airbags...

 

My 09's leafs were shot after 30k of moving some heavy stuff around.

 

A heavy duty leaf pack like Dakar's might be the solution. The Toyota springs are pretty weak

 

Normal for stock springs.

 

Normal with that many people in the back plus a tank of gas and you up front,thats about a thousand pounds.