David, these GSO made focusers can be a real pain in the bum. The entire useablity of the focuser is determined by those two small aluminium screws right along side eachother that sit underneath the draw tube. I have a dog of a time making real sense of these two, having had the same problem as you.
Best I can suggest, until someone with better understanding offers help, is to first deal with the screw furtherest away from the OTA (1 in picture below). Have it set a little firm. It will set the underlying tension & clutch in the focuser. Set it then don't touch it. The screw closest to the OTA (2), that is the screw you tighten or loosen to lock or free up the draw tube.
It is a bit of a trial and error thing to set up. I have this same focuser on my 8" dob - it is a GSO scope. In the dark I still sometimes twist the tensioning screw, and I have a female-dog of a time restoring things...
I hope this helps.
Mental.