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Hello Bruce,
I don't know American insects very well, but this one seems more like a member of the family Sarcophagidae to me!
Like I said, I could be wrong, and there are maybe Tachinids there that resemble Sarcophagids a lot.

And what is going on at the rear end: this is a male, and what you see is the genital apparatus, one of the tergites/ sternites bends down and back underneath the fly's belly.
And because it's red, it's clearly visible as a red knob at the rear end!
Greetings