Post away! Don't worry about being in the wrong place...
I've gotten my best mileage with these 'mods', best to worst:
1. Driving like a grandmother got me about 20%.
2. Avoiding high-alcohol and cold-weather gasoline got me a solid 5%.
3. Switching to a lower-ratio diff (3.73) and high-grade full synthetics helped a bit. I did that all at the same time so it's impossible to say how much each one helped. I wanted it to help more, but what can you do? Again, <5%
4. Cruise control made a bit of a difference too, as well as really hard 185 R14 all-season tires helped as well. Combined...maybe a point or two.
Those numbers are really hard to quantify, there is a wide variety of other factors that come into play. The best mileage I ever got was almost 44mpg. All highway driving, moderate altitude (500-3000 ft above sea level) & temperature (low 60's). I drafted a lot of trucks at 100 feet back or so with a lot of cruise control. My average according to GPS was only 61mph overall IIRC. If it had been a less hilly route I might have done even better.
I'll be trying some aero mods, like a rubber air dam and blocking part of the radiator opening next. I'm also considering a wideband o2 sensor, to really see what's going on. Finally, I've mixed a special low-viscosity coolant mix (66% water /33% coolant/water wetter) and I'll be putting in a high-temp thermostat with a matching rad switch and a fan delete. I'm also tempted to control the alternator off the brake circuit...prevent charging all the time, pulse it only when necessary.
FYI, every cold-air mod you do will decrease your fuel mileage. More air = more fuel burned = more power. For high efficiency, use warm air. It'll make the engine more efficient, but you'll lose a few HP along the way. I suspect fogging the airbox will make a lot of noise but very little else unless you have some head work, larger cams, bigger crank, etc. The stock filter box works very well IMHO, as long as it's clean. Same goes for the fuel & oil filters.
I pulled my P/S belt because the rack was leaking. It didn't make a noticeable difference in mileage, but it did help with the oil spots under the car. It makes the steering feel much better though - less numb on center, very direct. Feels "right," except at a standstill. Then it's a bit of a PITA, but not unacceptable. Bit of weight savings too.
