The gearing could be tested pretty easily. Have you done a mileage check cruising in 3rd gear? That would be approximately equivalent to having a 3.70 in the rear.
If mileage increases, then you want to change the gears. If it stays the same, then you may want to change the gears to make it more enjoyable in the lower gears. If it drops, then 2.73 may be ok but 3.70 is definitely too short.
After considering what Gary said, I do agree that 2.73 should do alright with that motor on the highway. My total ratio in overdrive is 2.33 (3.70 x .63). But it does not hurt to confirm with a simple test. It could still be too tall for city economy which could be dragging your average down. My city mileage is 11-12.
Lawrenceville, GA