I decided to pursue Physics independent of my course, a while back. I selected a few textbooks to study for this. And.. I could not come to "finish"[1] them.
[1] - By finishing, I meant to have devoted satisfactory time on each significant topic and generated an understanding of the subject.
Introductory physics books are constrained in that it is impossible to fully explain all of the topics without starting from somewhere. In the case that you do not understand how something works in its entirety, then that is to be expected. Otherwise, if it is the case that you find it difficult to complete problems within a timely manner in a given book, then you must simply do more problems.
At first, I tried being clever and read it all like a literature book. This clearly made me no sense. Then, I tried to focus more on individual topics and dug myself into an endless research hole. Then I strictly followed the book and practiced the back problems, which relatively was more effective. However, I tend to develop very slow this way and lose patience eventually, the book catches dust.
It seems you are not used to reading math books in general. Introductory physics textbooks are structured similarly to introductory math textbooks, so expect to read them the same way. Obviously, you would not read a math book like you would a novel, and obviously, you would not learn algebra before you could add. Technically, some physics topics can be learned by themselves, but for introductory physics that is largely irrelevant since you will have to learn everything before anyways to move on.
Dense topics like physics and calculus require a significant amount of automaticity in order to progress at an appropriate pace (see this excellent answer on Math Educators StackExchange by Justin Skycak). Conveniently, both introductory physics and calculus have the prerequisite of precalculus, meaning doing problems in precalculus will improve your automaticity in basic math, thus helping you greatly in both topics. If you do not master algebra and trigonometry, then you will surely struggle learning new topics as you will constantly be switching back and forth trying to recall how to do basic operations.
I also tried to cleverly "skim"[2] through the textbook, but faced a lack of background material to build on advanced topics.
Looking ahead to see what is coming next is actually a good thing, even if you don't understand it, as it gives insight as to what you are currently working on now could be useful. Again, however, that doesn't mean you should skip topics, and keep your reading on future chapters brief as to not lose focus on your current one.
Is my frustration and sluggish progression natural?
Maybe. Physics problems can take a long time to solve on your first encounters with them. But if you're struggling on 2D motion and basic forces, then I suggest you put down the physics textbook and go back to the fundamentals instead.
Is the use of textbooks solely, not recommended?
Lectures can certainly help a lot. In general, math and physics textbooks, particularly the "conventional" ones used by high schools and colleges, can be quite technical and are sometimes more akin to a "review" book than something you would learn from entirely by itself. That doesn't mean you shouldn't use them, but just be aware they aren't the only source where you can learn from. With that being said, pick one textbook and stick with it. Especially for physics, the differences between each textbook are very little.
Is it my lack of commitment? Could I be missing something in my attempts? Are there better methods to consume dense and technical academic textbooks?
Working by yourself through a textbook is more or less a matter of habit. Personally, I do problems as one of the first few things after waking up in the morning. Having a well-lit, accessible place, where you can work continuously without any significant distractions is also extremely important. I like to use my dining table for this purpose: it has an overhead light that does not cast any shadows, it is a short distance from my bedroom, and I don't get any hunger pangs since I'm right next to my kitchen.
All in all, working through math and physics textbooks is a rather linear process. Read the chapters, take notes, and do (all of, preferably) the problems. If you cannot do a problem or it is taking you too long, skip it and come back to it. If after coming back to the problem you still cannot complete it, find the process to the solution or get help. Finally, if you find that you are skipping and coming back to problems too often, you may be working too fast or too ahead. In that case, go back and practice more.