Changed the t-stat twice but still get minimal heater

Hello,

If the engine is warming up to the normal operating temperature and the thermostat is good then it is likely a clogged/restricted heater core.
Which might not be allowing the hot coolant to flow thru properly, and you are getting minimal heat.
You might be able to flush out the heater core, but if the clog is severe than you will have to replace the part.
The heater core is located behind the dash on the passenger side.

Be sure to only work on the vehicle when the engine is cold.

You might find these articles helpful:

https://www.2carpros.com/articles/how-a-car-heater-works

https://www.2carpros.com/articles/car-heater-not-working

https://www.2carpros.com/articles/replace-heater-core

I have attached diagrams for your reference.

Please let me know of any questions.

Thank you.