Percolation? Heat soak? Don't drive during summer??

Yea i have no clue about the heater core or if it works... want to know a secret??? I dont even know where it is lol. I'm assuming behind the dash, and that dash looks good where it is haha.
The hoses are all new (replaced with everything else), except for 1, ill replace it just to be safe, and ill put in this 180 thermostat.
I can help with that I just replaced mine haha. I'd just bypass it. Run a bypass hose and see if it gets better. A stopped up heater core will make one overheat.