Changing the sump filter requires a pan drop only and the filter pulls right out and new one pushes right in. Pan gasket needs not be replaced ( reusable many times over ). Spin on filter is changed just like the engine oil filter from the outside. PPE sells them or Allison. Do not buy from GM dealer as it will cost you triple.
Oh I forgot.
The spin on also has a magnet on it. It usually stays on the transmission but check just to make sure. It sits on the center of the filter IIRC