Re: Furnace too large?
The high temperature limiter cuts off the flame when the heat exchanger gets to hot then lets it turn back on when the blower cools the exchanger down to a safe level. With the furnace oversized it has probably been over heating and has been using the limiter as a switch turning the gas on and off on a regular bases. The limiter is not designed for constant use. One solution that may work is to connect the blower to run at a higher speed while heating.
Be sure you live your life, because you are a long time dead.-Scottish Proverb