[BMERDOC]

Your truck has a condition know as Tire Pull. The old alignment is now "burned" into the tread causing the condition. Swapping tires side to side proved this. The truck now wants to go left. If your tires are the same all the way around you do have the option of swapping one of the tires to the diagonal corners to see if the pull goes away (left front to right rear or vice versa). The only other option if you were serious about eliminating the pull is to purchase a new pair for the front. Aligning it again would not show any improvements. If you decide to mess with the shim packs to correct caster and camber you'll want to have the alignment rechecked.