What should be done first to improve the operation of a sluggish large self-operated gas regulator?

To improve the operation of a sluggish large self-operated gas regulator, lowering the inlet pressure is often the best initial step. When the inlet pressure is too high, it can lead to issues such as excessive force within the regulator, causing it to become sluggish or unresponsive. By lowering the inlet pressure, you can reduce the load on the regulator's diaphragm and allow it to respond more quickly to changes in demand. This adjustment can help restore proper function without necessarily requiring repair or replacement of the regulator.

The other options may not address the immediate issue effectively. Repairing the regulator could be a valid step, but it's more appropriate after assessing the pressure conditions. Raising the outlet pressure is counterproductive to solving sluggishness and could exacerbate the problem. Replacing the regulator might be necessary if it is determined to be faulty beyond repair, but it's generally more efficient to troubleshoot and adjust pressures first before resorting to replacement.