To get back to the original issue, does the trailer and truck feel like they are rising and falling together. I would describe porpoising as a rocking motion and not the issue at hand. My combo appears to rise and fall together and not have a rocking motion on the type of roads mentioned previously.
I noticed that the issue actually got worse after adding shocks to the trailer. All other handling improved with shocks. I suspect that the shocks are not allowing the springs flex as much. A trailer with longer, weaker springs might not transfer as much energy to the truck.
