Rear Derailleur Double Shifting - Shimano - Deore XT - 9 Speed - When I shift up or down the rear derailleur more often than not double shifts causing me to have to reshift to get to the gear we need to be in.

The cable has just under 1000 miles on it, the derailleur is not bent and has not been in a crash, I have been tugging on the cable to take out any slack and have tried different tightness settings...

Has anyone experienced this and how did you fix it?