Steering issue 1970 GMC 3500

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This truck has run about 150k miles and is new to me from original owner. On the 500+ mile run home on good roads, the power steering performance was pretty solid with very little "play" or "wander". But, on the final few miles of rougher gravel road, with some ruts, etc., the steering wheel tossed back and forth and it was harder to control in rutted/rough places.

I will get it up on a rack to better inspect all of the steering components for any troublesome wear/play (nothing significant found when inspected on ground before purchase) and will replace any parts as needed.

But, I suspect that there are no major wear problems there. So, two questions:

1. Might this be a common issue on rough roads with one ton trucks of this vintage and can it be corrected with a pneumatic "damper" (shock absorber?) on the steering cross link. A 69 K20 here with big tires had such a damper already installed when I bought it and it gives no such "tossing" effects.

2. Might this particular issue be centered in the steering gear box and can anyone tell me the best way to check for undue wear/play in that component?

All helpful info will be appreciated.