Duane...

Sounds like a fairly normal physiological response to increased activity, significantly (?) increased fluid intake, altitude (9,000' is significant if you normally reside around sea level or relative low altitude), and cold. By the 4th day it sounds like you had acclimatized. Our bodies do alter their responses to stimuli as we age.

I would suggest adding some electrolytes back into your diet. With that much fluid intake and lack of salty snack intake you're probably overwhelming your body with fluid causing an electrolyte imbalance. This will tell your body to shift fluids out. You may not have noticed a "performance" improvement with gookinaid, but I'm sure there were more subtle benefits from using it on hikes. I second the recommendation of Emergen-C as it is lightweight and easy to carry. You don't need to add it to all your water, but add it in periodically all day, even if you just mete out one pack throughout the whole day. Sodium Chloride is not the only electrolyte we need to keep in balance; calcium and magnesium are also essential, in addition to potassium (which is easier to obtain from food sources, like potatoes).

MNS

P.S. Your BP is definitely enviable. Most people don't really understand the value of maintaining a low BP. Your organs will definitely thank you!