PastorW. That load jerking you speak of happens in the truck/trailer pulling world too.
Funny but I found from experience that the more frame flex and tung flex you have the more jerking.

Bumper hitch trailers pull much smoother than goose neck. I have had a goose neck jerk so hard we got rid of it.

My bike trailers hitch at the axle. OR in the case of my kiddie trailer (Homemade Hitch) I attached it to the Disk Brake mounting holes just above the axle.

On the other hand, you may be letting the clutch out too quick,,,,,,,,,,,,,,