How to increase mpg

What gear ratio? Anything over 3.08 is a MPG loss with the ultra low rpm sweet spot capability of the D13 motor.
For best MPG on D13, you want to cruise between 1050 and 1300rpm. The lower end of the sweet spot.

Don't worry about the low rpm shifts with the iShift, the engine and transmission were designed to work together in harmony, you will certainly not hurt anything.

The Volvo D13 will pull far lower than a Cummins without hurting it. It holds Torque flat the whole way down to 1050rpm before it starts to drop off.

 

Can you give us your normal cruise speed, rear end gear ratio and cruise rpm as you currently operate it?

Thanks