2013 Sequoia HVAC Issues

Yes, this is a Sequoia, but should be basically the same as a Tundra and there are a lot more of you guys out there vs Sequoia owners If not allowed, please delete or let me know and I'll delete

I purchased a used 2013 Sequoia Limited. It had a full service history and one of the last times it went to service, I saw "customer says poor heat". Sure enough, couple of days into ownership, the heat is barely there. Here is what I do know...

1. Coolant is full(unless there is a big air pocket that's being stubborn). Removing the radiator cap it looks like the coolant is moving so that should eliminate the water pump/thermostat. Tho, it could be partially working

2. The mode selection works.. so when it's floor, it blows floor.. when it's front.. blows front.. defrost.. blows up at the defrost.

3. One thing I noticed, with everything synced(drivers/passenger and rear), the front is blowing luke warm but the rear is blowing ice cold even when the temp setting is set to "HI"

4. When I feel the heater core hoses.. 1 is hot for sure.. the other is not nearly as hot???

Where should I start? One friend said to flush the heater core?? Another said the dampers are not functioning right? What is the best procedure to diagnose the issue? Also, can the control head unit be sending the wrong info even if its displaying the correct temp i'm asking?

Thank you for any help!!