The weapon rotating slower than the torso of character when using IK to attach weapon to hands

I am trying to use IK to attach weapon to player's hand. This is my IK setup: Here the Right Hand Target is at the Trigger handle, while Left Hand Target is in the front. Here is my IKHandler code:

 public class IKHandler : MonoBehaviour
 {
     Animator anim;
     Vector3 lookPos;
     Vector3 IK_lookPos;
     Vector3 targetPos;
     PlayerContorller pc;
 
     public float lerpRate = 15;
     public float updateLookPosThreshold = 2;
     public float lookWeight = 1;
     public float bodyWeight = .9f;
     public float headWeight = 1;
     public float clampWeight = 1;
 
     public float rightHandWeight = 1;
     public float leftHandWeight = 1;
 
     public Transform rightHandTarget;
     public Transform rightElbowTarget;
     public Transform leftHandTarget;
     public Transform leftElbowTarget;
 
     // Start is called before the first frame update
     void Start()
     {
         anim = GetComponent<Animator>();
         pc = GetComponent<PlayerContorller>();
     }
 
     void OnAnimatorIK()
     {
         anim.SetIKPositionWeight(AvatarIKGoal.RightHand, rightHandWeight);
         anim.SetIKPositionWeight(AvatarIKGoal.LeftHand, leftHandWeight);
 
         anim.SetIKPosition(AvatarIKGoal.RightHand, rightHandTarget.position);
         anim.SetIKPosition(AvatarIKGoal.LeftHand, leftHandTarget.position);
 
         anim.SetIKRotationWeight(AvatarIKGoal.RightHand, rightHandWeight);
         anim.SetIKRotationWeight(AvatarIKGoal.LeftHand, leftHandWeight);
 
         anim.SetIKRotation(AvatarIKGoal.RightHand, rightHandTarget.rotation);
         anim.SetIKRotation(AvatarIKGoal.LeftHand, leftHandTarget.rotation);
 
         anim.SetIKHintPositionWeight(AvatarIKHint.RightElbow, rightHandWeight);
         anim.SetIKHintPositionWeight(AvatarIKHint.LeftElbow, leftHandWeight);
 
         anim.SetIKHintPosition(AvatarIKHint.RightElbow, rightElbowTarget.position);
         anim.SetIKHintPosition(AvatarIKHint.LeftElbow, leftElbowTarget.position);
 
         lookPos = pc.lookPos;
 
         float distanceFromPlayer = Vector3.Distance(lookPos, transform.position);
 
         if(distanceFromPlayer > updateLookPosThreshold)
         {
             targetPos = lookPos;
         }
 
         IK_lookPos = Vector3.Lerp(IK_lookPos, targetPos, Time.deltaTime * lerpRate);
 
         anim.SetLookAtWeight(lookWeight, bodyWeight, headWeight, headWeight, clampWeight);
         anim.SetLookAtPosition(IK_lookPos);
     }

Here is what is happening: video The character's torso rotates before the gun rotates. Also, in the beginning, the torso is rotated towards left. What is the reason for this? What am I doing wrong? I am new to IK.