Are you using the original CAB-1, or the newer Legacy CAB-1L?
Personally I always found the original CAB-1 to be quite vague, but as we know, these are desperate times. If you are using the original, when you turn the knob, look for a red light flashing on the black command base. Beyond that, make sure your base is plugged directly into a grounded outlet (absolutely no 3-2 "cheat" adapters!) And for best performance, no surge suppressors or long extension cords either.
One last thought... I know that it's possible to put Legacy locos into a "switcher mode," where the speed steps are cut in HALF for more slow-speed precision. If this is what's happened to your loco, the manual probably contains a process to set it back to "road engine." My $.02.