Check out this thread:
I have already been through this scenario and I would bet you have an issue with the dampener; however, I would start with a good brake bleed to see if this (hopefully) resolves the issue. If not, you will have to go with the UFP actuator. As you will note in my thread, the replacement process is very easy. I am more than happy to answer any questions.
A couple of tips / notes:
The test to see if your system is working is this. Un-plug your trailer lights. Attempt to back your trailer up (preferably a slight incline). If the system locks up, then you have a good system. IF it is jerks and jumps but still locks, it is likely a failing Reliable actuator.