2001 F250 steering column sensor help!

Hello. I have a 2001 f250 diesel 4x4 truck. Some days I can drive completely normal down the road and other days it darts me to the left and right and is hard to stay on the road. But after a little while it goes back to its normal mode again. My dads mechanic told me it was the steering column sensor. The auto parts store and the ford dealership have no idea what I am talking about. The part isn't listed. Has anyone else had an issue like this or changed one of these before? Thank you!