Y does my car keep overheating ifvwe change waterpump, thermostat, and fans

Possibly air in the cooling system. Are you sure there are no coolant leaks? Sometimes air pockets will get in the cooling system and cause overheating. A company called Lisle makes a special radiator funnel to bleed radiators of air. It's about $30 on Amazon. I'm pretty sure Altimas (the 2.5 at least) don't have bleeder valves to do this so you must use a funnel. Check out videos on youtube.

Did u put thermostat in right side up , head gadgets?? Air bubble purge system.