Recent SOC behaviour on cross-country trip

I just drove about 1200 miles each way for the holidays, from Springfield, MO to Salt Lake City, UT, and back. On the trip out I took I-80 across NE and WY; on the return trip I drove I-70 thru Colorado and Kansas. I've owned my 2005 fully loaded Prius for about 3 months now, bought as a certified pre-owned from the local Toyota dealer with 56,000 miles, now with 67,000 (I also have a long commute).

I'm curious (and slightly worried) about my observations of the SOC of the hybrid battery during my trip. It's my understanding (from John1701a.com) that the method in which Prius climbs most hills often leaves the battery with a higher SOC at the end of the climb than at the beginning, and my own daily observations (on my rather hilly commute thru the Ozarks) bear this out. So I was a little concerned that something was wrong with my Prius when the SOC sat well below what I'm accustomed to seeing during the cross-country drives.

Driving west thru NE and WY there are some periods of significant climbing, and my SOC sat below the halfway mark more than I've ever seen, at times sitting in the red for long periods (or dropping into the red) even while the energy monitor indicated power flowing into the battery. I was worried that something was going wrong with the inverter or system that monitors and controls the flow of energy. (I remembered efusco's recent comments about grill blocking causing his inverter temp to spike in 40-ish temps; and in fact before leaving on the trip I removed most of my grill blocking to be safe, leaving only the top upper and the bottom lower slats blocked). Once I arrived in Salt Lake City, however I again observed "normal" SOC behavior (better than half full, usually between 6-9 bars), and the SOC continued in the familiar patters during my 2 week stay.

Driving back, I opted to take I-70 thru Colorado, which needless to say involves some serious climbs, two of which are particularly steep and long. On both of those climbs, the Hybrid battery was completely drained, dropping to only one red bar shortly into the climb. I backed off my speed considerably to see if Prius could find the "sweet spot" that would allow it to slowly charge the battery during the climb, but to no avail.

The other odd thing I observed is that on the trip out, after cresting a hill that had left the battery completely drained, the SOC remained essentially empty for some time during the downhill coast, then suddenly and quickly reached a "full" SOC -- much faster than I've ever seen before. From empty to full probably took less than 30 seconds. I'm not sure if this is what the battery actually experienced, if there's a lag in the SOC display due to the way the SOC is measured and reported, or what else it might be, but between the low, extended SOCs and the hyper-fast recharge, by the time I reached my destination I was worried that something was wrong. Only the normal operation of the car during the 2 weeks I was there (and since I've returned) makes me think that the car is probably fine, and that I was driving under exceptional or unusual circumstances that gave me the strange readings.

My question to the group is: do I need to be concerned? Is this normal? Did running the Prius with such a low SOC potentially damage or shorten the life of the hybrid battery? Do I have possible inverter or other electronics issues? I'd particularly like to hear from anyone who drives Prius in or around Denver, Vail, or other mountainous regions to see what's "normal" for them.

Thanks in advance for all replies, and thanks for reading a long post! I love my Prius!