What are the 3rd and 4th tier schools?

Wih a 4.0 and a 31 ACT, you don’t need to go into third-tier schools, let alone 4th tier.
Pretty much any national LAC ranked 40-125 will work, plus your flagship(s), regional universities ranked 1-15, and private universities ranked in higher numbers than your flagship (so, if your flagship ranks 40, numbers 41+).