ok on my s10 i have lowered it 2" (purely for looks) cost was about $160 (coulda gone cheaper but i decided to go the better route, can cost as low as $30)

i have installed underdrive pullies and they are well worth it (smaller lighter crank pulley and smaller alt pulley) i noticed a bunch more torque and gets up to speed faster. and noticed a 1-2 mpg gain in normal every day driving.

its a truck its meant to haul stuff (ie its gearing is setup to do so) you WILL NOT notice any difference by removing ~90 lbs of a tire and jack.

i did notice (yes this goes aginst alot of stuff ppl say) that when i built my toneau cover that mpg went up by 1 not to mention gained a whole lot of storage thats secure and mostly dry.

DRAFTING i was shocked when i drove 3 hours to chicago behind a charter bus and made it there on 3 gallons...

Now that you mention it, some trucks can be lowered for free by removing lift blocks from a solid rear axle and de-cranking torsion bars on an independent front suspension. However, you should check with a forum for that truck to find out if there are any negative consequences, such as driveshafts at bad angles.

I wonder about the big gaps around the tires and the fenders if closing them off more would help. Lubrication improvement is one place that should help a lot. What about the roof rack??

yes the s-10 extended cabs need angled lowering blocks so the pinion angle doesnt change. regular cab needs flat blocks. (2pc driveshaft on ext cab single shaft on reg cab)

i put some oversized mudflaps on my s-10 that go up far into the wheelwells and it may hav had an effect but not much if any... i have thought about making some sort of rear pan and side pans underneath but not sure i it would help at all...

Some of your questions have already been answered, like the potential cost of lowering, and on thinking of what type of exhaust mods to do- straight "performance" exhaust is probably not the way to go.

But to clear up some things, the picture of the toyota was posted earlier in this thread, here it is again.

https://www.evworld.com/images/pknox_toyota.jpg

take a close look. There a a number of aero mods you can see from this picture alone. And there are articles on this site and elsewhere that talk about this vehicle, you've got to look.

And you've got to look to find out about the underdrive pulley's. google is your friend.

As for lubrication there are a handfull of good ones, and i personally use LCD inc. products

And one last thing, there seems to be an interesting new 'feeling' or 'theme' to the posts on this board since i last posted here some time ago; there is this feeling that if a mod is potentially 'negligible' in it's affect on mileage i.e. the calculations on weight reduction come to mind, then it is seen as to not be 'worth it' or whatever.

I've always been of the opinion that if you're going to do this mileage "thing" you need to always be looking at ways to help, never worrying about the hard numbers each mod impacts mileage, but more the sum of all parts- the knowledge that the general principles of better mileage will succeed, and the more improvements you make the better, even if 'better' is marginal.

So go ahead and tape off the vehicle, take off the spare (while looking for anything else to dump) add aero mods, mess with the engine, mess with the tires, try new driving techniques, and don't stop, and especially don't think that one or two things are going to get you to where you're looking to go.

extraordinary results are from extraordinary efforts.

chesspirate, you make a good point...I generally look at ideas critically with a focus on whether it is worthwhile or not, but really, it's worth experimenting as long as the cost is negligible too.

The whole cost thing is dependent on the vehicle owner for sure. I've seen people blow a LOT of money on performance mods and i've heard of a couple of people spend a LOT of money on efficiency mods, just depends on your priorities, we all have our magic number.