I’m with the rest of the guys. You have to check the basics. These trucks have some known issues like KTM and blue mentioned at the steering box.
Steering gears will develop slop, rag joints get loose, ball joints and tie rod ends get loose. Add in some wiped out crappy twin tube lift kit shocks and you have a recipe for crappy handling.
As blue mentioned, get someone to crank the wheel back and forth while watching the steering box. Only the pitman arm should move. If the whole box is moving you probably got some cracks in the frame. Tug on the rest of the steering links looking for play. Check leaf spring bushings too. Jack the axle up and check ball joint play with a pry at under the tire.
While you are there also pay attention if there were any steering correction parts added to account for the lift. A 6” lift could have a raised steering arm on the drivers side knuckle, dropped drag link and possibly a dropped pitman arm or any combo of the two or three. Without correction you’ll end up losing steering throw in one direction because the steep angle from the pitman to the steering arm is reducing the length.
They can handle at speed when everything is taken care of. I can haul down the road at 85mph with one hand on the wheel in mine. But everything is fresh since I’ve gone through it all. Fresh steering gear, frame plate to fix the cracks, ORD steering box brace to prevent future cracks. Upgraded xj intermediate shaft to eliminate the rag joints, raised steering arm, fresh ball joints and a single monotube stabilizer and Bilstein 5100 shocks on all four Corners. I didn’t do all that work at once, but as things needed addressed I fixed them.
Once it’s all set, a good alignment dials it in. If your caster is low I’d bring it up to at least 4-6 degrees.