Follow the advice by "Wrenchbender Ret." to make sure that you don't have a dangerous problem. If everything checks out, then try adjusting the steering box using info in the Chevrolet Shop Manual. I assume that the GMC box is the same.
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1954 Shop ManualHere is a recent post on the subject ...
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StoveboltYou MUST disconnect the Pittman arm to adjust the steering box. Advance AutoParts will loan a Pittman arm puller to you for free.
I bought this fish scale to measure the drag in the steering:
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WalMart fish scaleI hardly drove my truck for ten years because the steering had a quarter turn of play. Then I read my Shop Manual and followed the directions. Now it's a pleasure to drive. No play in the steering.
If the simple adjustment doesn't work, you may need to rebuild the steering box. I'm sure that other forum members can help you.
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Chervrolet Steering Box manual