Can I ask, was it the thermostat you replaced or the radiator temperature outlet sensor?
I have the same issue with cool air coming out of the left hand side, luke warm mid and slightly warm on the driver's side, have tried vacuum bleeding and still no joy.
I don't think there's an issue with the engine thermostat myself, but the rad sensor could well be duff, or more likely I damaged it during the first flush which is when the problems started
Cheers