Hey Chip,
It finally registered that you replaced the calipers & rotors.
So here's another suggestion: check the right rotor. Compare its braking surface appearance to the left one. My thought is that if the left one grabs, it should have at least some slight vestiges of wear. If the right one still looks untouched, then that says the problem is in the brakes. If the right and left rotors appear equally used, then the problem is probably is somewhere outside the brakes.
Make sense?
Tom