coverage between two buildings that are 60 feet apart

I just upgraded to fiber optic internet service and I am still having some internet issues.  I have no cell service where I live except for wi-fi assist.  I need solid wi-fi in both buildings without having to string two fiber lines.  I currently have a 5 year old Nighthawk X4 7500 with a Tether range extender in the outbuilding.  I am thinking of upgrading or otherwise changing things up but just know enough to be dangerous.  Anyone have any suggestions on what I can do to boost my current equipment or suggestions on upgrading to get more solid and reliable wi-fi?