Thats around what i'm getting with my 89 3.0 auto running 488's with 38's if i manual shift & stay out of o/d i can get around 14 mpg. you need to change gearing to get more mpg. I think you should be getting better than 12 mpg though there might be other isues you need to look at. tune up time.I just bought 529's and front & rear E-Lockers & headers 'i'm hoping this will get me alittle more mpg.