Replacing a existing slab door from house to garage
You do not want to replace a 1 3/4 inch door (which is presumably a solid core door) with a 1 3/8 door of any type. The reason is that fire codes require a door with a fire break rating between the house and the garage. Fire break doors are generally 1 3/4" thick for standard doors. 

Many homes now days may even use a steel clad door in this application instead of just a solid wood door.