There is a Balance between Gross Vehicle Weight, Tire Pressure, and Tire Wear. Built up or Stripped XJs will not Weigh in at Stock GVW and may need to have the Tire Pressure adjusted Accordingly for On Road Driving. IMHO
On Road and with my Build, I have my Tires filled about 5 psi more than Stock Recommendations. On Trail and in Sand, I Air down to 15 psi and I find that Works Best for me.
If by Rubbing the Tread in a Forward and Backward Motion you feel Chopping or Cupping, you may have something going on that should be Addressed as soon as possible. Causes of this Type of Wear may be Improper Mounting of the Tire on the Wheel, a Tire that is or has become Out of Balance, Bad Shock Absorbers, Incorrect Air Pressure, or a Defect in the Tire itself. Worn Shock Absorbers will not cause the Wear by themselves, however may Contribute to the Wear because they can no longer Hold the Tire to the Road Surface Correctly.
Hope this helps.