AX-15 is a manual. AW-4 is the automatic.
your gas mileage will be what your gas mileage will be. results will vary, but it will likely get worse no matter what you do now. 33s are harder to push around, plain and simple. but there's no sense in worrying about your mpgs. just drive it like an old man and you'll be ok. :thumbsup:
but make sure it's running to its full potential. do a tune up if you haven't already and fix the vacuum lines. :thumbsup: