Effy,
As you can see and read, you're certainly not alone in this type of situation. Been there, done that, several hundred times ourselves on trips etc. The first thing that you have to realize is, people are people. Everyone is born different on this planet. The three "Cs" have just about been eliminated from much of our society.
The first "C" is, Common Courtesy, and, again, you've experienced it several times over. The next "C" is, Common Sense. How much of it do you see on a daily basis, not much! The last "C" or, you could say, "CD" is, Common Decency.
Driving has always been labeled as a "Privilege", not a right. And, taking that privilege and not having it co-inside with those three "Cs" is, for the most part, a "common" every day occurrence. Now, what do I do in your described situations? Well, I try and be as courteous as possible when driving, right at, 62' worth of machinery. I know and realize that folks many times, don't want a "wall" in front of them and, they don't want to be slowed down.
So, I try and take advantage of clear spots in the faster lanes and use them to advance my position, based on needs at the time. But, there are times when, based on driving conditions, up-coming grades, 18 wheelers that I can see waaaaaaaay in advance that they are proceeding at a much slower rate than I will be, etc. and, and other considerations that, I must "AGRESSIVLY" move into the faster lane and make my move.
What many folks, I'd say actually maybe as much as 90% of those folks out there in regular "Car land" have never, EVER driven anything like what we're driving and, have never experienced tactical driving needs, i.e. calculating speeds needed for grades, up or down, and, stopping a monster load like what we're all driving, turning what we're turning, and all that, so, they are absolutely CLUELESS about what kind of effects they have on us when they pull their inconsiderate moves. Others, are plain and simple idiots, PERIOD! Those are born every minute.
So, while many of us try and present a good image as motor home drivers and, try to be considerate and courteous, there are times when, we must take matters into OUR hands and do what we have to do, in order to advance our travels at a safe and efficient manor. If people get P.O. because I had to aggressively move in front of them 'cause that gap was the only one I knew I had a chance to take so I would not loose momentum and, was approaching a half dozen slow moving 18 wheelers, well then, that's life. I suspect they'll get over it.
Scott