to Turtle: Thanks for the great advice.
My math shows, from a difference of one mile per gallon:
(figures rounded to closest whole number):
150,000 miles / 22 miles per gallon = 6,818 gallons x $3.05 = $20,795.
150,000 miles / 23 miles per gallon = 6522 gallons x $3.05 = $19,892...