Steering Problem - Rover Discovery

My '97 LandRover Discovery shakes considerably when I drive over any bump at a speed over 55 mph. The front wheels and steering wheel shakes and continues until I slow down under 55 mph. The steering box and rod has been replaced. Any suggestions, the mechanic is clearly fishing to solve the problem at this point

Is there a steering damper on this vehicle? If so, perhaps it needs to be replaced.

You say “the steering box and rod has been replaced.”

Rod? What rod?

Yes, the steering damper and bushing was replaced; I got it mixed up. The mechanic recommends replacing the tie rods and steering coupler.

I concur with you mechanic’s recommendation. Replace the pitman arm, inner & outer tie rods. Those parts will be at end of life for a 10 year old Disco.