(performs weakness analysis) I fully support your decision to switch out Sandshrew because, with it, you have a 3x weakness to Water. Without it, you have 2x weaknesses to:
Bug (Tyranitar, Alakazam)
Electric (Charizard, Gyarados)
Ground (Luxray, Tyranitar)
Rock (Charizard, Gyarados)
Water (Charizard, Tyranitar)
Also, if your opponent uses Gravity you will suddenly have a 3x weakness to Ground due to Charizard.
I thus recommend that Sandslash's replacement not be weak to any of those types.