Re: very cold master bedroom
Sounds like you need a HVAC pro in there. you likely have poorly installed or improperly designed duct system that's not delivering heat to your master bedroom. Are the other bedrooms cooler? Have you tried leaving the door open? Can you feel a lot of air trying to get under the bedroom door? Where is the thermostat located?
NExt you could try partially closing a few registers in rooms that are warmer. Make sure the registers in your bedroom are open fully. IF you can access the ductwork form the basement or attic, make sure it's attached and not collapsed.
Worst case you may need ot modify the ductwork and add another register to that room along with adding dampers on the other branches to the other rooms.
To make matters worse, it's possible that your furnace is oversized. An oversized system will make temperature differences worse.
All rooms in my house after I balanced it and made some modifications are within 1 degree F except the kitchen that's 2F cooler. I decided that it wasn't worth cutting another duct at this point.
1925 Two-Story Stucco Beaux Arts Neoclassical