Modifying Gravity for Local Player

Hello everyone - I'm working on a personal project that involves a character moving around a horizontal cylinder while moving in a set direction. The gravity for the character needs to be constantly pulling them towards the center of the cylinder (which does appear to be working correctly), but when I move the character along their forward vector, I am seeing it 'slide' either farther up (+Y) or down (-Y) the cylinder.

If I remove the forward movement, the character stays oriented correctly and doesn't slide in either direction (which is what I would expect/want). As soon as I do though...well, hence the problem.

The object's rigidbody has all rotational axis locked, and I am not using gravity.

Any insight or help would be appreciated.

Thanks!

Code Snippet:

     //----------------------------------------
     // Class Variables
     //----------------------------------------
     // Private
     private float _RotationSpeedMod = 1f;
     private float _RotationSpeedBase = 120f;
     private float _RotationSpeedMax = 165f;
     private Vector3 _VecGravity = new Vector3();
     private Transform _MyTransform;
     
     // Public
     public float _RotationSpeed = 0;
     public float _Gravity = -9.81f;
     public float _MovementSpeed = 10.0f;
     public float _MaxVelocity = 2.0f;
     
     // Awake
     void Awake()
     {
         _MyTransform = transform;    
     }
 
     // Update is called once per frame
     void Update ()
     {
         // DeltaTime Value
         float DeltaTime = Time.deltaTime;
 
         // Rotate Left
         if (Input.GetKey(KeyCode.LeftArrow))
         {
             transform.RotateAround(Vector3.zero, Vector3.right, DeltaTime * _RotationSpeed );
                 
             _RotationSpeed += _RotationSpeedMod;
             if (_RotationSpeed > _RotationSpeedMax)
             {
                 _RotationSpeed = _RotationSpeedMax;
             }
         }
         // Rotate Right
         else if (Input.GetKey(KeyCode.RightArrow))
         {
             transform.RotateAround(Vector3.zero, Vector3.right, DeltaTime * -_RotationSpeed );
             
             _RotationSpeed += _RotationSpeedMod;
             if (_RotationSpeed > _RotationSpeedMax)
             {
                 _RotationSpeed = _RotationSpeedMax;
             }
         }
         else
         {
             _RotationSpeed = _RotationSpeedBase;
         }
     }
 
     // Physics Update
     void FixedUpdate()
     {
         // DeltaTime Value
         float DeltaTime = Time.deltaTime;
         
         // Compute Gravity Vector
         Vector3 VecUp = _MyTransform.up;
         Vector3 VecFwd = _MyTransform.forward;
         Vector3 VecTemp = new Vector3();
         float GravityRate = _Gravity * DeltaTime;
         float MovementRate = _MovementSpeed * DeltaTime;
         
         Vector3 VecGravity = new Vector3(VecUp.x * GravityRate, VecUp.y * GravityRate, VecUp.z * GravityRate);    
         Vector3 VecMovement = new Vector3(VecFwd.x * MovementRate, VecFwd.y * MovementRate, VecFwd.z * MovementRate);
 
         Debug.Log( "VecGravity: " + VecGravity );
         Debug.Log( "VecMovement: " + VecMovement );
         
         VecTemp = VecMovement + VecGravity;
         //VecTemp = VecGravity;
         
         Debug.Log( "VecTemp: " + VecTemp );
         
         _MyTransform.rigidbody.velocity += VecTemp;
         
         Debug.Log( "Vel: " + _MyTransform.rigidbody.velocity );
             
         // Limiter
         if( _MyTransform.rigidbody.velocity.magnitude > _MaxVelocity )
         {
             VecTemp = _MyTransform.rigidbody.velocity;
             VecTemp.Normalize();
             VecTemp.Set( VecTemp.x * _MaxVelocity, VecTemp.y * _MaxVelocity, VecTemp.z * _MaxVelocity );
             _MyTransform.rigidbody.velocity = VecTemp;
         }
         
         Debug.Log( "Magnitude: " + _MyTransform.rigidbody.velocity.magnitude );        
     }