Great post.
Everything has already been answered here, so just my two cents. While many people do just show up and get it done, there are so many subjective factors to consider it really just all depends. Don't take this the wrong way, because I' ve been there, but it sounds like you are still trying to see what works and maybe have not trained "properly" for yourself, however you would subjectively define that.
I know the feeling, trust me. As Fit2Climb said, you are going to have to find your system and see how it works for you, which you are doing by asking on here. You can check my first trip report
here when I did Whitney in the winter. I didn't put in a ton of information about fueling or energy, but it was not good. On the way down my stomach was not happy with all the non real food I was giving it; so I learned that "real" or light food works better for me. Bob Pickering and myself also did the mountaineers route a few months later....same thing. I came down off the final 400 and my stomach started telling me to stop eating this packaged crap right now.
I spent years running all around the mountains at some long long distances in a day, hiked all around, and what not, but it was not the same. Did the cardio base help me? Oh hell yeah, but its different. I have certifications in training and nutrition, but these do not translate until a new system is made for a new environment. My biggest issue on the Whitney at first was fueling, as i said, hands down.
For most people i think what Fit2Climb said is best: its a proactive strategy in fueling and preparation but also having a good "first gear" or cardio base where you can go low and slow for a long time on all terrain.
Also, as others have said, sleeping high. You will notice a big difference if you do that. I would argue if you change your diet strategy, sleep high for two nights, and work on your cardio base, you will have a great chance.
