I agree, something it wrong with your Mach 1, My Lincoln Mark VIII LSC with the DOHC 4.6L, 4R70W, and 3900# curb wieght got 27-30mpg with 3.23 gears and 27-28 with 3.73's in it now. Hell, taking it easy In town back and forth to work I average 20-22mpg.