Oldsmobile/Buick Repair: Buick Heater, buick park ave, digital thermostat

Question
I have a 94 Buick Park Ave with a V-6 3.8 engine.  Recently with the onset of cold weather I have been using my heater.  My car has the digital thermostat in it where you increase the temp by degree rather than the little slide mechanism.  Recently, I have been having a problem with the heater.  I generally like to keep the car set at about 80-85 degrees (F) during cooler temps, but it seems that on this setting, only cold air comes out...almost as if the A/C was on.  When I put the temp to the hottest setting (90F), then I get the hot air back again.  This is true wheather I use the heater or defroster.  Is this a thermostat problem, and if so, is it expensive for a garage to repair?  If it is of any significance, my digital exterior thermomether (that uses the same display screen as the thermostat) went on the fritz a few months ago...It will register 125 degrees out when it is only in the mid 60's.

Answer
HI MIKE.WELL COULD BE A T STAT.BUT REALLY DON,T SOUND LIKE IT.ESPECIALLY IF YOUR OUTSIDE TEMP HAS PROBS AS WELL.I WOULD RECCOMEND A T STAT AND IF NO HELP THEN PURSUE POSSIBLY A BODY CONTROL MODULE OR BCM.T STAT RELATIVELY INEXPENSIVE ABOUT 1 HR LABOR AND LESS THEN 20 IN PARTS.LET ME KNOW I CAN HELP DIAG THE BCM PROB.  PLESES TAKE A MIN OF YOUR TIME TO RATE MY HELP  TY BILLYMAC