97 1 ton Chevy dually pickup

This pickup has a hard shaking on the steering wheel at speeds between 25-35mph.

The tie rod ends are firm, new ball joints, and nothing loose in any of the steering apparatus. After 40mph all shaking is gone. Have discussed this with other mechanics and cannot find the problem.

Possible start of a tire separation?

2 or 4 wheel drive?

There certainly lots of possibilities.  How about rotating the wheels front to back?  See if it goes away or changes the way it feels.  If so you have pined the problem to a wheel or tyre.

If this has a solid front axle, any loose or worn component can result in this shaking. The technical term is “shimmy” and even components that appear to be tight or not excessively worn can trigger the shimmy.

Be sure to check the alignment and try to keep the alignment within the inner half of the tolerance.

I vote for rotating the tires! That always fixes my Jeep. the more agressive the tire the worse it gets.