BioMax
+1y
You guys all have the right idea, but are leaving out an important part...
When your truck is going straight and your steering wheel is centered, the steering box (or rack) should be in the center of it's mechanical limits. If your steering wheel is off by a spine or 12 you will need to turn the box further one way to center the steering wheel. By aligning the truck to center the steering wheel and not fixing that issue, you will end up with one tie-rod arm being longer then the other. This will cause the wheels to bump-steer differently than each other and make for a very strange driving truck.
Most good alignment shops will check that the wheel and the box are centered before performing the alignment. You can do that same by counting the number of turns it takes from lock to lock and find half way. If your steering wheel is not centered, there is your problem. If it is centered, you need an alignment...BAD!