I’ve noticed when someone else stops pumping at the station it speeds up. I think they are all connected and the main line has a maximum output. At least at my Sam’s Club they are definitely that way.

It’s probably just one pump/motor per physical stand and if both sides of the stand are used at the same time you get half the flow rate since you’re sharing it with your neighbor.

If it’s busy and slow, it’s likely because pumps share lines and the pumps aren’t sized for the number of spots. It’s also obvious when the pump speeds up after someone stops.

If it’s not busy and it’s slow, then it’s a maintenance thing and the pump is in need of service.

I worked at a gas station about 20 years ago, so things may have changed since then. When our pumps started running slow, it was almost always due to the pump filters nearing their end of life. They would get clogged with the minerals and sediments in the tank.