Reply #3: They look a LOT smaller

[TrogL]

The existing pipes were 1/2" copper (does that sound right?) direct to the taps with no shutoff.

This was replaced with shutoffs (I think they're 1/2" but look smaller) then about 9" of braided pipe that looks like it's 1/2" outside but must be much smaller inside but that could be an illusion.

I thought about air in the pipes so I ran the water at 1/2 strength for quite awhile but didn't get any interruptions.

The plumbing in that end of the house is quite complicated, though.

Upstairs, hot and cold to kitchen sink, T off the hot to a dishwasher. Directly downstairs there's a laundry tub with taps and hot and cold leading to the clothes washer. Right next to that is the hot water heater.

I'm wondering if it's something crazy like flexibility in the hoses leading to the clothes washer combined with flexibility in the hoses to the kitchen sink are causing some sort of pressure imbalance.