Towing 3.5 Ton - balance question

Towing with a gooseneck trailer with two 7,000 lb axles. With an 8100 lb mini on it plus 4000 lb trailer weight the trailer pulls well and stops well. However, downhill or on the level, any dips in the roadway or other imperfections causes the trailer to jerk the truck fore and aft...annoying. I can either speed up a bit or break...either of which will greatly reduce this jerk resonance. The question is, do I need to position the excavator differently on the trailer, forward or back, to minimize this annoying resonate jerk? I can test a different position; but chaining down three points and making a few test runs would take some time, which we are all short of, and energy...short there too!

Is everything tight? Neck adjustment, hitch in the truck etc? Some trailer and load combinations seem to do that regardless of load position. I do also wonder sometimes when you're close to the trailer capacity if you're not feeling the neck and hitch deflect a little. It's annoying for sure. Add in everything being spring ride doesn't help. Make sure nothin is broke..... mark the trailer and try a different spot each time. Just don't get too light on pin weight. Don't want the tail wagging the dog!

Junkyard

what size truck?

Three quarter ton. Minimal towing but a bit jerky.

I have the same problem . I just add a little trailer breaking and it takes the for and aft out of it . A bigger truck would help .