I don't believe this to be true, or I suppose I would require evidence for this claim that I haven't yet encountered in my life. I find when someone claims that "America used to be so much better" they're completely discounting the experience of all the people who weren't born into or existing in privilege or within the US "in-group."
The US has always been distrustful of the indigenous people already inhabiting the North American continent, of newly arrived immigrants, of black people, of single men. Single women were sometimes witches and murdered for it and only recently trusted enough with their own personal freedom, which is being curtailed again. Atheists were never trusted.
I really don't think the US was ever a "high-trust" society and there doesn't seem to be any evidence or foundation to claim that it was.