Performance issues with my NightHawk EX7300

My extender is in my house about in an adjacent room fro,m my router. When I have my laptop in that room I get speeds between 50 and 80Mbps.  When I take my laptop out to my garage my speeds vary each day. Some days I get 60Mbps, some 18Mbps and some 1.2Mbps. My garage is about 18 feet from my house and the Nighthawk extender. Has anyone experienced these sort of performance issues? could it be releated to weather??? I called tech support but that conversation did not go anywhere. any ideas out there?