Ed -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. Now, in last week I was coaxed to r/r fuel eff module. Fine, I paid$160 and mpg went to about 50. Overnight, it dropped to 43 (never was I that low) and stayed there at 43 last 4 days. Did you experience such drastic fluctuation? I own a 08 Prius.