far from being or having expertise in interpreting HRM data, and groping through my info as I go along...
I might offer a few comments, based on similarities I see, or things that are not shown...
1. your time in the lower zones is roughly 3.5 minutes for not even one mile covered. It might be worthwhile to 'warmup' a little longer before plunging into the heavier workout. Without considering age (which is a big factor), your workout might actually improve if you were to warmup for 2.5 - 3 miles, roughly 8-10 minutes. Warmup for me is between 120 & 130 bpm.
Worst thing to do is roll into the garage with an hugely elevated HR and heavy breathing (both for health and 'recovery'), better to back off the last .5 mile (1 mile is better) and step off the bike with a heart rate round 100 and breathing that is back to 'normal'.
2. Spending almost 9 minutes in your 90-100 zone seems proportionally very high. This area being well above the AT, if your zones are set correctly. My guess is that your MAX HR setting might not be properly judged. HR numbers during the ride won't change, but where they fall will prolly be more 'accurate'. Try to find your real MAX HR or guessimate damn close to it. I wouldn;t think, from this data, that 175 is it...
3. Noting that this is 19.4 mile 'loop', and that you're 'climbing' 1926 ft (correct?); given an average slope (just picking something...) of 7%, that means that 5.2 miles or better than 25% of the ride is done in some sort of climbing or uphill mode - that's quite a bit of climbing considering the ride length. Maybe not a true climbing ride, but also certainly not just rollers (unless they're non-stop). This have further implications...
as for climbing type, its best you tell us if its mostly even grades or some typical Eastern backroads steep, shorter pitches.
4. Based on the idea of 'climbing' quite a bit, I believe you'll have a hard time bringing down the HR, as other's have suggested doing, on this route. Unlike moderating on even or rolling terrain, climbing always causes spiking of HR and if you're climbing in Zone 3 you'll likely feel as though you're about to fall over from lack of speed. Note the drop in speed in Zone 5, thats a pace avg for climbing hard and short descents... 3 minutes climbing and 40 secs descending like a bat outta hell.
5. To my thinking, finding the HR range where one reaches heavily beyond the Anerobic Threshold (AT) is an important bit of info. Time spent just below that range continues to develop cardio & muscle aerobic abilities. Time spent heavily Anerobic has minimal value (maybe none) in pushing up the AT, and may be useful in accustoming us with pain and how to deal with it for necessary periods. Ultimately, the more time one spends aerobic, the better the overall ride performance will be.
maybe find another circuit that has considerable less climbing and see how that goes... maybe after you reset the MAX and zone ranges...