So looks like I have to replace my heater core

Also try to replace any of the old foam seals that you can get to.

The flat one on the fresh air door. The ones around the doors, heater, etc. that will help keep the air going where it's supposed to be.

When you put it back in, make sure to get the hook set for the fresh air area, then put the studs through the firewall and secure all of them after they have all been started. Also make sure that you get the drain tube for the evaporator through the hole if that part was removed, otherwise the condensation from the A/C will get in the interior/carpet....