I somewhat disagree in regards to mods NOT helping mph. Of course you have to get past the point of testing the gas pedal to enjoy (test) the mod. Once you do that, I believe you do indeed see an increase in gas mileage.
Now whether you ever get back your intial cost in gas saved over the life of the vehicle would be determined by how long you own the vehicle, but my experience has been that with about $1500 in mods (tune-exhaust-cia) I've seen 1-2 mpg improvement in town and 2-3 on the road. Again-I have to keep my foot out of it, but I believe it not only improves the efficiancy of the vehicle, but adds power when needed for towing, or the "fun stuff".
I think once you get past those few mods you are packing in more power, but the efficiency may start going backwards. Just my .02

 

It can be done. But, you might have to commit to driving it for a long time to see the payback. My 6.0 was doing 11.5 to and from work, and 13 on highway trips like the one I did Saturday. My stroked up 6.6 gets 13.5 to work, and pulled 16 Saturday on the highway. Even with a few buried speedo passing events. I fully beleive that when Allen tunes me, it will go up further. The oversize l'up clutch faces in the soon to come Fuddle 'verter, should also help. Ya gotta know though, I have spent a ton already.
As for gas prices, we need to get the oil family out of the whitehouse. And, as for "riceburners", this man would prefer to walk. To each his own. I'll get off the soapbox now.

 

SLOW DOWN!!! I drop 2 mpg going from 60 to 70. Forget the oil covered air cleaner, I have had my race car on the dyno many times and never got any HP increase fron a K&N over a new stock paper element. Use 5w30 oil. Exhaust may help a little but how many miles would you need to recover the cost? Bigger tires hurt. 4.10s suck ( my wifes YD gets 2 mpg better than my SD) I haven't tried it but synthetic gear and transfer lube could really help. Any more ideas?

Dan

 

The home depot/Lowes CAI mod! Best bang for your dollars right there!

I just stole my mom's Saturn, she knows where its at if she ever wants it back