First of all, in answering a comment, from M&C in Palm Springs, (where they reminded me it's in the 70's out there, :-P) do you really think I'd be here at 0 degrees instead of Palm Springs if I had a choice? But there's always that little thing called money. And the cost of taking the time off. (since I don't make money when I don't work)
I know, I take off all that time in the summer, so ya, it's all about choices. But for what it'd cost to go out there for one long weekend, I can take 5 long weekends here. But thanks for thinking of my well being. :-)
Now on to the mysteries.....
Like I said, I replaced the furnace filter, and shortly after that, the temp was where it should be. I went in yesterday morning, cranked it up to 72, and with-in an hour or so, it was at 72. So apparently, the filter was the issue. I even put the old thermostat back on and it still maintained the temp. Now we have had a bitter cold January, so maybe a slightly clogged filter was enough to block the airflow enough, causing it to shut off after a period of time. I'll continue to monitor the temperature and see. :-)
Now the card in the door. Come to find out, even though the address on the card is a P.O. box out in East Lansing, Their physical office is just a half mile or so down the road. I live in Clinton County, (just barely) and just down the road is Ingham County. The road I live on changes as it goes from one county to the next. Where it's called North Grand River Ave. in Ingham County, It's West Grand River Ave. in Clinton County. Sooooo, that means just 1/2 mile or so from my house is nearly the same address as mine, except with north instead of west in it. We had numerous problems with people looking for our house when we first moved in because of the similar addresses. The owner of the business card thought some of his mail was going to the West Grand River address instead of his North Grand River address. Why he was thinking that, I never did get a clear answer, and my address number isn't the same as his. But he didn't know that because our address is on the mail box post, and it's covered with a big snow bank, so he just guessed that I was the one. He is now corrected on that. :-)
Mystery solved. :-)