Did you solve your issue?
I would use a directional yagi antenna. There are instructions floating around on how to make one cheaply using a Pringles can. You can then unscrew one of the “rubber ducky” antennas off your router and attach the pringles can using a “pigtail” (coax), and point it to the garage. That should put a signal right where you need it without brute forcing power into an omnidirecitonal antenna that blankets the whole block.