SHould I replace my 10 year old oil furnace with gas? Is it going to be more cost efficient down the road? T

Yes and no. It really all depends upon the price of the fuel. Oil burners have faded away in some areas like where I live but in others like northern climates they are still popular.

Oil prices are many times unsteady but gas prices can also fluctuate especially propane. The old gas type furnaces used to run a long time before needing service but not anymore. The newer high efficiency gas furnaces are a bit more trouble prone than the old ones they have replaced.

With oil you still need to tune up the burner once a year and change the oil filter.

The nice thing about gas is there is no more oil smell in the home when the unit is serviced. I used to hate that smell and after working on oil burners all day my wife made me take off my cloths in the laundry room so the smell would not get into the house. I remember those days from 40 years ago just like it was yesterday.

A gas furnace should save you some money on your utility bill especially is you opt for the 90+ model.