Need help. Not sure if having problem with stat or furnace. Stat was programmed to 68, and on "Auto", but furnace kept running past 79 and non-stop. I turned off the stat but it still heated up till the circuit was shut off. I left it off for at least an hour then clicked it back on. This solved temporarily.

You could either have some wiring that is exposed (so check wiring all the way through for bitemarks or anything if you can) and also examine your relays in the circuit. If one sticks it will cause this to happen.