Lube is your friend. The shift rod that comes out of the steering cable and connects to the motor's steering bracket should be shiny and smooth looking like a hydraulic ram. If it's gunky or corroded, get to work. Wire brush off the loose gunk, clean carefully with solvent, then rub it with emery cloth until it feels silky in your hand. Then apply a film of lithium grease to the shaft in several applications, working the steering wheel back and forth to ensure all the shaft is covered. You should also remove the cable from the gearbox box up behind the wheel and follow the same process with the grease, using the motor end of the cable to work it back and forth. You should at this time take a grease gun to all lube points on your motor. There should be grease nipples for the horizontal pivot that allows the engine to tilt up, and the vertical pivot that allows the engine to pivot left and right. Add a dab of lithium grease to the end of your shift and throttle cables and their pivoting connections inside the motor cowling, and any other bushing type moving items in there - cowling release catches often get missed.
All of the above is worth doing every spring. There might be one more item causing your original problem - steering cable routing. Check carefully along the cable's entire length from helm to transom that it is supported but not constricted or kinked. Pay special attention to where the cable makes the turn from running along the gunwale to exiting into the transom/splash well area. As well as a substantial direction change, this area often has batteries and other equipment that may have not be properly mounted and could be impeding the the cable during tight turns or heavy sea conditions.
