EZ-est MPG gain is FREE
 

I have an 03 Echo/Toyota. started using a Ultragauge. I noticed the EZ-est way to increase my mpg's was to follow an 18 wheeler @ 2 seconds distance. I have noticed 20-40% increase in MPG's on the hiway. A scangauge will work just as well. Check the instantaneous MPG behind an 18 wheeler for a few miles on level hiway, then pull out for a few miles you will see an amazing difference. And its free. Let a big truck or bus break the wind for you. Even an SUV will help. If you do the hiway, you don't even have to go slow on long trips, get 2 sec or less , (2 sec is legal) behind a fast one and you will notice a great increase in efficiency. I went from about 37 up to around 45-55.

yes and more likely you will get a steering wheel halo . no the smartest thing to do but is well known around here. search is your friend and so is the 65+ mod list.

no thanks, my life is worth more than slightly better fuel economy. also if you do that alot, you will have stone chips all over your car including the windshield

But (as has been said many times before) if you drive on California freeways (and presumably those in Texas & many other states), you're inevitably going to be following some vehicle too closely, because if you leave anything like an adequate separation, one or more cars will cut into it. That being the case, there are advantages to the lead vehicle being a semi, in addition to the windbreak effect. Most semi drivers are less disposed to sudden brake application, if they do brake they'll probably decelerate at a slower rate than a smaller vehicle, and if all else fails, most have those nice bars across the back to prevent you running underneath. And of course you don't have to worry about hurting a carload of people.

40% seems generous for trailing 2 seconds behind. That number seems closer to what I was seeing when I was sandwiched just a few car lengths behind a semi. Regardless, as with almost anything, your mileage will vary.

I would be more worried about the rocks that end up cracking the windshield..

Great for economy, but could be a death trap.
On a side note, I did read a studythat was exploring various ways of reducing fuel consumption on trucks & trailers, one of the things they looked at was slipstreaming as described in post, using two trucks close together and computer controlled, they found both vehicles actually benefitted in improved economy.
But until we have better response times for sudden braking, or flying debris as mentioned, better to stay away from this type of behaviour.
It also irritates me when people pull in close like that, it's a personal space thing.

I can break wind just fine. ( yes - immature I know )
Using a truck to do it is dangerous.

I wouldn't call it free if it adds so much risk.

But the point is that it doesn't seem to add risk, at least under the circumstances in which most people drive.