Shader-related stretching in 3D models usually comes from mismatched UV mapping—when texture coordinates don’t align with the model’s geometry.
UVs are how 2D textures wrap onto 3D shapes; if they’re stretched (e.g., from poor unwrapping or scaling), the shader (which applies the texture) will display the texture as stretched on the model.
To fix this, re-unwrap the model’s UVs to match the texture’s aspect ratio or use UV editing tools to smooth out stretching.