First, make sure you dont have any play in those little u- joints from box to steering wheel. Also check for play in those slip joints. Do you have the 1 to 1 ratio in your angle box at bottom of steering column? If you still have the manual steering ratio of 1 1/2 to one, this will increase hunting. If a slip joint is sloppy, take shaft to a location that fabricates pto shafts. They can make up a new one. Dont tell them it is for a steering shaft, as some won't touch it due to "liability". If all that is ok, increase the caster some more. Maybe 3 degrees is only less due to age and axle twist. Too much positive caster will increase steering effort, regardless of power steering. We went through all this several years ago on our 4104. When done, we had one inch or less play at rim of steering wheel.