Power setting and big tires

[89Vette]

Updating with info from tonight's full-tank refill:
15.5 MPG
70% highway driving
Power Mode OFF
CEL still on

Power Mode is now ON for this tank, but I'm not sure I'll be able to replicate the city/highway split.

-V

Yeah,,,that's a toughy. What diameter of tires are you running?