First thing I do is to eliminate the tires:
1) Check pressure
2) Test
3) Swap sides (yes I know about directionals, this is just a test)
4) Test again - any change
5) Inflate to 40 psi
6) Test - any change

If there is no change with different inflation and after swapping sides, it is probably not the tires

Next worn bushings and/or ball joints can make alignment change when stressed. Will read perfectly on the rack but change when driving. This can also cause abnormal tire wear.

At 70k I would not expect such wear but depends on the coditions of the 70k - if 10 miles a day on a dirt road in southern AZ all bets are off.

"Gotta be something in that steering box that centers the pitman arm "

Actually not really, it is the amount of caster angle that is dialed in that centers the steering. PS just reacts to input forces unless broken or clogged. If you feel the steering is pushing at you, flush and refil the PS system.