Key changes made:

1. **Physics interpolation** - Now interpolates between previous and current physics states using the accumulator alpha value. This eliminates visual stuttering from fixed timestep physics.

2. **Increased physics rate** - Changed from 60Hz to 120Hz for smoother simulation with smaller steps.

3. **Max steps cap** - Limits physics steps per frame to 4 to prevent spiral of death on slow frames.

4. **Re-enabled matrixAutoUpdate** - The manual matrix updates were causing issues; letting Three.js handle it is more reliable.

5. **Removed redundant traverse updates** - No longer manually updating child matrices every frame.

The plane should now move smoothly without stuttering.