Any play in the steering gear or linkage can cause wander, as can toe setting. Check your tie-rod ends, drag link ends and Pitman arm. In addition, 4x4s have a chronic problem with cracking the frame rail at the steering gear mount, causing the sensation of "herding" the vehicle. Thoroughly inspect for cracks around the gear mounting bolt holes. If cracks exist, they will need to be drilled, v-grooved, welded and dressed; then reinforcement plates can be added as well as a frame rail stabilizer (torque arm that controls rotational flexing of the rail). Kits are available.