05Prius92

I was on here a few months ago wondering why my gas mileage had dropped in the winter. I learned that a cold battery has less power than a warm one. Also, Milham Toyota dealer coaxed me to r/r a Fuel Efficiency Module. I paid $160 for the FEM part and labor. Within 3 days my monitor showed 52 mpg. Great I was so excited - that was same as when I got it in July (last summer). Now, as if overnight it show 43 mpg - I've never experienced that low mpg. Any one have similar fluctuations from one day to the next? Frank