Our pump must be one of the older ones because it has only one adjustment screw that just regulates the shut-off threshold.
I spoke with Reace yesterday and he said to play with that adjustment and see what happens. Well, backing it off counter-clockwise caused the pump to run continuously if the faucet was on or off. I tried to turn it clockwise but found it was already turned all the way in i.e. there was no more adjustment possible. Reace said they do this at ETI. So, diagnosis is a bad pressure switch. Reace is sending up a replacement pump. Apparently, the new one will require adjustment by me once installed because it has some sort of internal bypass that the current one doesn't have.
I apparently am the first one, according to SHURflo, to have a pressure switch fail. Go figure.
We're still have'n fun...