It seems like your body (and others) just need more days to adjust at that intermediate altitude. You now have a good idea of where your threshold is.
Also suggest: back off on the eating. In addition to nausea being part of AMS, the need for fuel is often overexaggerated. The crazy, young marathoner might need 6000 calories, but most of us, especially going slower and taking more days, don't need to eat the whole pie. For a short trip like Whitney, you can lightly graze on some carbs, and burn your fat stores as needed.
No problem doing this unless you are on Denali for three weeks. Far, far, far more people who "run out of gas" on Whitney do so because of AMS, not hypoglycemia.
