[Strodder]

That's normal for the shims to be that much different from side to side. That's a good idea with the string around all the tires to get your toe close. A good alignment machine, and tech will set the alignment to the centerline or, called thrust angle of the truck. A 4 wheel alignment is a must. Your rear axle has to be square with the center line first, then adjust the front caster, camber then the toe. If your rear axle isn't correct the truck will crab, and that will make your steering wheel off also, plus will ware your front tires because you will be compensating the steering wheel to go straight. That means when you turn the steering wheel your front alignment will be out of specs. I hope I didn't confuse you.
After the alignment is done and your steering wheel is still 180 out, turn the shaft at the rag joint, then you might have to go back and set the toe for the minor steering wheel adjustment. I hope this helps you understand how an alignment should be done. I've been doing alignments with the best alignment equipment out there since 1970. I also sold and trained techs after they bought alignment machines when I worked for Snap-On.