Hey man...yeah, there are pretty extensive sections in the book on driving without brakes and driving under load. The braking chapter started out as one of the shortest, since, really, what else is there to say besides "Don't use them?" Eventually though, I wound up expanding it to cover situations where you HAVE to brake (red lights, traffic, ect) and how to identify and avoid those situations.
Far as driving under load goes, I found that it depends on the engine, vehicle and transmission. The difference in BSFC under full-load (100%) vs part-load (25%) is generally the greatest at really high and really low rpm...the two are pretty close to equal right around peak torque. So, as long as you're within a couple hundred rpm of peak torque, then it doesn't matter as much if you're under full- or part-load.
But, all else being equal, power production and use is ultimately the deciding factor. The amount of airflow (throttle) going into the engine determines how many horsepower you're making, and BSFC determines how efficient those horses are. So, you don't necessarily stand to gain anything if you cut BSFC in half by loading the engine, but have to double airflow to do it. It's a balancing act. I've found that driving by load seems to work best on engines that have a really high torque peak (where BSFC is about equal regardless of load) that you never see under cruise conditions with your vehicle's gearing. In cases like that, yeah, it generally makes sense to trade off some extra airflow for an increased BSFC.
That logic would seem to stand up pretty well in your case, since even the LH8 5.3-liter in the GMC Canyon hits peak torque at 4,000 rpm, and the inline-five peaks at 4,600. Weirdly (or maybe not) the four cylinder peaks at 2,800, so it would seem to be a little less sensitive in terms of driving under load. BUT (and understand I haven't seen a dyno sheet for any of these), my guess is that the four-cylinder's torque and BSFC drops off a lot faster than either of the bigger engines...so, there's a good chance that it would work better going by load at low rpm. And considering your mileage, I'm guessing you have the four cylinder.
The only way to know for sure would be to find a BSFC @ load graph for your engine. The bigger the difference in load-variable-BSFC at a given rpm, the better off you are going by load. Of course, those charts are kind of hard to come by...I had to do some hunting to find a few for the book, and those were just for random engines of different types. But, a typical BSFC chart (measured at 100 percent load) will give you some idea as to how quickly it drops off on either side of peak torque. Generally speaking, the quicker it drops off, the more sensitive your truck is to load.
Just a little aside: I used to have an '85 Mercury Cougar with a 500 Caddy engine that I called my "12 mpg car." It got 12 mpg, no matter what you did to it, where you drove it or (for the most part) how you drove it. I didn't understand it at the time, but now I know it's because, with that car's gearing and the 500's table-flat torque curve, it never really strayed far from BSFC under full load. Which was good, because it didn't exactly stay under full load for long (when it did). So, as long as you didn't rev the hell out of the thing, it pretty much got the same fuel economy all the time. But that car was horrifically overpowered, and stripped down to about 2,800 lbs even with the Caddy engine. So it didn't care what you did. Your truck (assuming it has the four cylinder) is just the opposite.
And that's my thought on that
(PS: Approaches change depending on whether you have a manual or automatic. DWL works best for the manual because you can vary load by changing gears yourself. With an automatic, you're better off driving by the vacuum gauge once you're under way.)