On my 01 dodge my over head computer puts out the correct mileage, tempt, but on avg mpg and current mpg its reading like high 20's and low 30's. I know this isn't correct. I have 35in tires on the truck an the previous owner went through the abs side of the computer to change the tire size so that the speedo is correct. Anyway to get my computer to read accurately?

 

One you start adding boxes the overhead will never read right again.