Thanks for the suggestions but the problem is water pressure at the spout is varying so the supply line from garage may be too small or some other reason pressure is varying even if no other faucet is on. Doesn’t make sense but could it be if sprinklers and showers are all going on the block less pressure to go upstairs bath tub? Simple work around is great showerhead that works well with low pressure. My uncles place in North Carolina has high pressure in bath tub with big showerhead almost as good as gym showers that drench you in 5 seconds.
