THere is sometimes an adjustment for friction at the side of the control handle head. SOme are easy to adjust , some not. Often a screw head that appears to have no other purpose such as holding a cover in place is the adjustment.
Sometimes there are parts that need to be replaced. That's the case with my older Morse unit. The cover comes off and there are some plastic bushings and washers that must be replaced when they wear too much which of course requires a bit of disassembly.
If your control head is a Morse unit you should be able to go on line and figure out which unit you have or if you are lucky the thing may be marked under the cover. They made a lot of them. Then order parts.
And before I forget check the clamps that hold the cable end barrels, both ends. If those clamps are loosening the whole cable end may actually move a bit causing a change.