Is this true? The .44-40 used to be loaded to .44 Magnum levels?

Not quite. 44-40 rifle loads claiming 1800 fps were loaded at one time, but chronographs weren't then what they are now. I doubt if those old balloon-head cases could have handled that sort of pressure. But there were hot rifle loads that couldn't be used in revolvers, and people actually paid attention to the warning rather than blowing off their hands and suing the manufacturer! Times have changed.