Ford F350 axel ratio 3.31

I have a F-350 6.7 4/2 with a 3.73 and pull a 5th 39 + inches or just say 40 feet, weight 16,500 with no problems and get average towing of 12-13 mpg in low hills you know overpasses and such. Have got in 15-16 on level road of 20 miles are so. Works fine for me. Running on hwy empty normally get 19-23 regularly. Just my two cents worth.:)