On 7/8/26 driver pulled up on shot pattern at 9:30 am. Placed the truck in park and exited the cab using 3 points of contact. As EE was stepping off the last step to the ground EE felt EE's back stretch. The last step off was higher than normal due to uneven ground conditions. Driver didn't notice any pain that day. Progressively got worse after 5 days (7/12/26).