Most steering tabs on lower units are sacrificial anodes. They will dissolve as intended, and will over time completely dissolve if any stray current is present. Surface area is critical to compensate for steering rotational torque.
Check yours compared to new.
Another possibility is that the tube bushings are binding where the steering cable slides through on the engine bracket. With the boat on the trailer and the engine OFF, have someone press on the cavitation plate with their foot to apply pressure forward, as if the motor was creating forward thrust. Try the steering and see if their is any change as pressure is increased on the cable.
Also check to make sure that the boat is trimmed level. Port to starboard, not bow to stern. Take a long level and place it across bow while you are idling and the steering is easy. Check again at a speed that creates hard steering and make sure that the vessel is still running level. Some hulls, on plane at speed, especially aluminum, will change the running angles due to deflections on the hull below the waterline, created during construction, as well as stumps, etc. Trim tabs were invented to compensate for these factors. You may be able to shift weight, ie. batteries, fuel, ice chests, etc. Also check to see if you are running with a full live-well (water) that may be located off the centerline of the vessel.
Lots of factors translate into steering pressure, hope it is an easy fix.
boatstall
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