i notice a change when i rotate mine too. i think it is due to the different wear front to rear, but i haven't seen any bad wear. i rotate mine between 5k-7k depending on when i get around to it!
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2001 QC LB 4x4 HO 3.54, boost/pyro gauges, B1-2-EX4, F1 Mach3, Smarty, Blue Chip FMS, ConFE, DSS, 4.5" lift, 37" Toyo M/T, Airlift airbags, Thuren track bar and crossover steering