Heater Issue

I have a 2005 Tacoma & the temp. gauge shows it is at the normal mid range, but the air blows cold. Then it will start to feel warm so I turn up the fan speed and it thinking its getting warmer & it is actually still cold. Then magically at no particular time the heater works and is blowing hot air. I assume it is not the thermostat since the temp gauge is correct. Any helpful tips would be appreciated.

 

Im running into a similar issue. Looking forward to updates from you. Im digging around possible reasons.

 

Thermostat sticking. Dash gauges these days are an on/off switch. Assuming nothing else has been done to system, assume thermostat