Lots of people get side tracked between chucking and normal bounce. Chucking is the pin sliding for and aft in the hitch upon takeoff and stopping or just the trailer scooting back or forward by hitting a bump or expansion joint and the effect feels like a yank back or push forward in the truck.
The bounce effect is from the truck sitting on the helper or overload springs and bouncing up off and back down onto said springs...like jumping on a trampoline and hitting the ground everytime. Airbags help with this problem. Also as stated above the hitch putting more weight aft of the axel hurts as well.