I'm having the same problem. I'm at 50* for heat as well. My regal is a 93. I can hear the vacum for the flapper and it sounds like it is woking just fine. I just had the heater core replaced as there was a hole in it. Thought that would be the end of it but I thought wrong
. It sucks as I work in a northern part of ontario which is known for cold weather. My next step is to replace the thermostat. Now, after reading your post, I might be up the creek
as it didn't work for you.