Also, I was using a .30-06 with 180grain. I'm sighted in 1" high at 100 yards too
Going to the range isn't going to solve this problem for you. Steep angle shots (up or down, it doesn't matter) always require you to hold for shorter distances. That actual horizontal distance to the target (with a additional small factor for bullet air-time and BC, if you want to get really fancy). The above post with the trigonometry is spot-on. I'd bet you airmailed that 180 right over him.