Personally, I would say you could get a lot more out of this trip by doubling up zoos that are relatively close together and small. At least for now, it looks like you are going to have a few days with not a whole lot going on other than a small zoo and a relatively short drive. It would open up extra days to add more zoos or other things you'd like to do.
Obviously all people take different amounts of time at zoos, but for example, my sister and I did the Amarillo Zoo, Hillcrest Park Zoo, Spring River Zoo, and Living Desert in Carlsbad all on the same day back in 2022. While you are also doing the Carlsbad Caverns on the day you do Living Desert, Hillcrest Park and Spring River are the only things you have listed for those days and I'd be surprised if anyone can spend more than 2-3 hours at them. Similarly, we did Alameda Park Zoo, a couple hours in White Sands, and El Paso Zoo all in the same day. You may have other things planned, or be one of the ZooChatters that can spend all day at even the tiniest of places, but my two cents is that you're going to be looking for things to do on some of these days.
(EDIT: I've always used Snowleopard's trips as a guide when planning out timing as he often says how long he spent at a facility. While sometimes I'm faster than him and other times I'm slower, I've found it gives me a good base line and starting point. If you have his book, those times often feel like an over estimation for me.)
My other comment on the itinerary would be you are adding a lot of extra drive time to your itinerary, but I assume you know this as you are the one who planned it and have a reason for it. I, personally, would make the trip much more linear (ie flying into San Diego and working east and then fly home from Texas or vice versa), and just eat the extra fees that come with returning the car rental to a different place (for me the couple hundred dollars you are saving on this is just not worth the extra time, and gas money for that matter, you will be spending on the road).
Only other heads-up I would give is that you may want to have a back up plan/make sure they are open when it comes to the National Parks and any other federal properties. A quick Google search says physically accessible areas (ie roads, trails, lookouts, etc) are open, but things like visitor centers, campgrounds, etc., are closed. While I would hope this shutdown ends by January, you just never know with the way it is currently going.
