Have you taken your steering wheel off lately? You need to park the truck with the steering wheel straight ahead, pull the wheel, & re-position the cancelling block so it lines up with the steering wheel: 3 indentations matching 3 bumps (can't remember which is on the wheel). The holes/bumps are not spaced equally, so it takes a bit to figure out which is up on the block.
Then you carefully replace the steering wheel so it engages the cancelling block properly. If that doesn't work, the block is probably hosed.