For such a common problem, no one seems to have come up with a solution for bucking/chucking that works in all cases.
1. Definitely it's a result of resonance at particular frequencies, so adjusting your speed is an instant solution when driving over pavement joints, but it's less successful when driving over more random bumps.
2. Anything which stiffens the suspension helps. It might make bumps more noticeable, but that's usually less irritating than chucking. So this includes transfering weight to the front of the trailer or rear of the truck, higher tire pressures (within safe limits), tires with stiffer sidewalls, firmer shocks.
3. I've never tried one, but I think the special pin boxes designed to reduce chucking can be hit or miss. They work in some cases but not in others. In some cases they can make things worse.
So the best approach is to start with the cheap/simple fixes (adjust speed, shift weight, adjust tire pressures) and then progress to the more costly ones.