Why won't the Z82 lock on the pin quickly and accurately?

I'm getting pretty tired of using the Z82 to lock on pins for ranges. It takes forever for it to lock on the pin, and half the time it says it has a lock, it has actually locked on something else in the background. Every round, my buddy has to correct my ranges at least twice because the Garmin has "locked on" something ten yards further. Last week, I shot the range at 165 yards to the pin. My buddy said it should be closer to 145. So, I double checked and it locked on again at 165 yards. I tried a third time, it locked on the pin at 165 yards. Turns out, it was 145 yards. I don't know why it doesn't lock on pins very well. Any thoughts?