Wobble in front end has me baffled

I drive down the road at 25-40 mph and the steering wheel wobbles like the dipsy doodle for the old timers here. I have replaced the Idler arm, all
tie-rod ends, checked the wheel bearings for wear, replaced all four shocks as they were totally depleted. It got a little better after changing them and now it has gotten even worse than before. I have new tires on the truck. I took it to the dealer they put 4 new tires and rims on the truck from another truck for testing purposes and it improved it a little but it still was there. It is gradually getting worse.
What else is there that could cause this, the steering gearbox?
1997 Chev C1500 2wd LT1 Original Rims
Thanks
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nbt wrote:

You may have what I call a "caster death wooble" When the caster is set incorrectly for the vehicle tires load the front end wants to ocsillate/shake at times. Regardless of alignment specs (if you juat had it aligned) you need to change the amount of caster in front end. So if you have not had it aligned, get it aligned and if they say alignment is good, have them ad about 1 to 1.5 degrees more caster to front end. Make sure toes is correct too. This is a alignemnt issue.
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How much play in the steering gear? Is it wobbling or is it that you can't hold a straight line?

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Check the ball joint in the end of the Pitman arm.( Attached to bottom of stearing gear box) My son is restoring a 63 Falcon and you can get about a quarter turn in stearing wheel before anything attached to this arm moves.
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