Phil, welcome to the forum! What part of Texas do you hunt?
On the camera sensitivity, yes you will tend to get more false triggers during the summer, and yes by turning up the sensitivity you can invite more false triggers. It is a balancing act that you can only acheive with a little experimentation with your cameras.
The PIR is looking for contrast. Body temperature on a summer day is not much of a contrast to outside air temperature, so the sensor has to be set higher to see the contrast. Vice versa is true during the winter.
Here's how I look at sensitivity on my cams. Right now I'm using a some homebrews & a Scoutguard Anthony & Bill graciousily sent my way to play around with. Neither of these cams have any sensitivity issues in terms of picking up targets. So, I adjust my sensitivity not so much to avoid false triggers, but more to eliminate triggers on animals that too far away for night time flash pics. The same setting in the summer has less range than it does during the winter, so I move my settings with the temps. You need to "chase" the temps...higher temps, higher sensitivity...lower temps, lower sensitivity.
Good luck and I look forward to more Texas pics!