I have a problem with the cabin of my Mercedes 1993 2.3L 190E. With the tempertature outside <35F and the temperature on the climate control is at the highest setting, the blower speed at maximum and the engine temperature at 80C, the temperature in the cabin is cool, especially at highway speeds. At the lower blower speeds the temperature is hotter but not like before.

Things I have tried to remedy the problem are: changed thermostat, auxiliary water pump, heater valve, and forward, reverse flushed the heater core.

Any suggestions on what to check next. The in-car temperature sensor seems to read the correct resistance for the current cabin temperature.