I'm from TX too and I can tell you from experience that running flat ground won't do much for you in the mountains.What’s y’all’s preferred way to prepare for the backcountry? Being from Texas the way that seems to help me the most is running, I try to stay in shape year around but if I do go on a break the way I start out is running a mile every day for about 2 weeks then increasing to 2 miles a days under 15 minutes then by the time Im about to go on my hunt I’m up to 3 miles a day trying to keep my time around 23 minutes this helps to keep my heart rate rising which I’ve found is the best way for me to prepare for the mountains this year I’m goin for 4 miles a day
Best thing I ever found was running (not walking) bleachers at the HS football stadium. Over and over and over again until you find your limit. Then do it again with a 1 day rest, then again and so on. Running bleachers is the closest thing you'll find in Texas to actual conditions in the mountains. And the hotter the better.