If you can, pull the dragline loose before centering the wheel, so you know for sure you are centering the gear box and not the wheel stops on the axle. Over time someone may have adjusted the wheel stops incorrectly, this will make the steering box seem out of adjustment, so the steering wheel is moved.
If the truck drives down the road with the steering wheel off center, and you are reasonably sure the tight center adjustment is right, then the wheel is just installed incorrectly. But, if the center adjustment ( tight spot ) is off to one side, the axle locator pins, steering arms, or spring hangers are most likely in the wrong spot.
I never could get mine to center while driving, I finally made a adjustable drag link to dial in the straight ahead adjustment. My truck is a mishmash of parts from different years.
