It really depends on the type of trust you're talking about. You're right that in many places in the US, people generally act honestly. But that's not always true -- porch pirates are still a huge problem in cities, for example.

Policy-wise, I would not describe the US as "high trust" relative to the rest of the first world. Virtually all of our non-senior welfare programs are means-tested or require some proof of virtue (e.g. "I am actively looking for a job" to collect unemployment insurance), meaning that society broadly does not "trust" people to collect benefits honestly unless they're seniors.