Steering issue - 70 GMC 3500

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Bought the truck with about 150k miles on the chassis/susp. On the 500+ mile highway run home the steering performance was solid with very little "play" or "wander". But, now on rougher roads, with ruts, etc., the steering wheel tosses back and forth in rutted/rough places.

Inspection shows no troublesome wear/play. So:

1. Might this be a common issue 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?

3. Other thoughts?

A similar inquiry got no replies on the "Suspension" forum. All helpful info will be appreciated.