What is happening is that your trailer electric brakes are coming almost full on even when you are only lightly braking on the TV. When you ease up a little on the hydraulic TV brakes, the electric ones totally release suddenly, and give you jerking. The cheaper brake controllers do not have any type of resistor to give you trailer braking in between full on and full off. The better ones do, hence the elimination of the problem with a controller upgrade, such as Crabman's Tekonsha, mentioned above. Hope this helps.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.