A plastic lower air dam will help. Like the one in this pic:

 

I get 17 MPG out my lifted 89 pickup. It is on 35's and has no front plastic air dam on it. I have tried it with and without them with ZERO difference in mileage. On stock tires, my truck got 19.5MPG with a crappy flowmaster muffler and stock convertor. I put a topper on it when I redid the exhaust so no idea what I could have gotten out of it. It should be back to stock tires and no lift in a few weeks. I will find out then.

On the GMT400 trucks, I have only seen the front "skid plate" have an effect on cooling and mileage. Can't really say how much really, but I know made a difference.

 

Interesting. The way I understand it, any time you can keep air from flowing underneath your truck and creating turbulence, you should be reducing drag and as a result, in theory get better gas mileage. Read this article in Hot Rod about it and found it pretty interesting: http://www.hotrod.com/techarticles/b...d_effects.html

 

In a lower application, I think you would see a benefit. But these are 4x4 trucks on tall tires. There isn't enough there to have any effect. If the plastic dam came down 18-24 inches lower, you might see some effect, but 5 inch thick air dam on a truck with a front bumper that is 24 inches high or taller, isn't really effective. It would have more effect on the cooling then anything else.

Look how far it is off the ground on my truck when it was stock

and on my stock 97 tahoe

 

Valid point, but I figure they put it on there for a reason, it would be cheaper for GM to leave it off.

 

On the 2wd I would say it was there partly for mileage and more so appearance. On the 4x4, I think it was more to hide the low hanging suspension points and to make the front of the trucks match. Compare the pictures I posted above to see just how much suspension is visible.

Also, standard tire size on the GMT400 4x4 was a small 245/70R16 that seemed to measure out about 28 inches tall, but the aluminum wheel option included 265/75r16 which kicked the tires up to around 30-31 inches tall. That being said, the standard 4x4 didn't really appear any higher then a 2wd, but how many did you see sell with the standard steel wheels? My new suburban was sold with steel wheels as it was a factory W/T truck, it sits very low even on 265's the PO installed on it. That makes me wonder if they didn't raise the truck up slightly for the 265's from the factory.

 

I plan to lower the truck someday and will look for a valance for sure. Looks and potential reduction in air drag.

I need the rear seat because of the kids. I most often have only my three kids so I could take it out, but it is too much of a pain to load and unload it, not to mention storing it somewhere. I have taken out the spare, jack, and the rear carpet(cargo area) was gone when I bought it. I have taken out about as much weight as i can yet keeping it family friendly.

For the trip air pressure will be up to 80 unlike my 55/65 for reasonable ride around town.

 

be careful with running higher pressure so as to not wear the center of your treads faster than the outsides. you'll also have less traction should you hit some rough weather


...not that you don't know that already

 

Good point to be made, I am very aware seeing I do tires for a living. The tread wear and proper handling is why I generaly run the proper pressure.

 

so how far south you coming? i could use a set of Firestone Destination A/Ts