[cleanspeed1]

I would do a couple of things, the first being a mass air conversion for the efi. That will take you from the batch fire / speed density to a sequential system. Ford Motorsport used to offer the system and no doubt can be found from one of the late model Mustang vendors. That one change will pick up the mileage quite a bit. Then I would call dpTuner up and see about a custom tune. Jody knows what he is doing.

The exhaust system from the motor to the tailpipe needs to be dealt with, and I would get a set of Doug's tri-y long tube headers, 2.25-2.5" piping for the rest of the exhaust
, high flow catalytic convertor, muffler and full length tailpipe.

As far as the other changes are concerned, if you get the tune right and drop the gearing down to 3.08 or 2.73, you will not have to give up the A/C and the power steering for a mileage gain. Couple that with the aero mods and you should be good to go.

If you want to do a maximum effort, full size Ford, it'll be better to start with a 2wd, 6 cylinder, stick, base model truck with fuel injection and then mod it from there. Unless you really want to do an engine swap on the existing truck, it'll be a lot less work going with a truck that's already set up that way and a lot cheaper.