[tomfoolery]

From where I sit, and I'm not an RF expert, it appears that the only thing you haven't replaced is the preamp. With 2-edge signals at your location, it's entirely possible that a working amplifier with a low noise margin may have been just enough to make reception on many channels reliable. An amp isn't a substitute for antenna gain, but I've seen plenty of folks post here that adding an amp added channels, suggesting they were just weak enough at the end of the cable to be unreliable unless a little boost was added.

Since antennas don't normally fail 'hard', to paraphrase GUM, but amplifiers DO, and it's the only thing you haven't tried, that's what I'd try next, if it were me.

Also, your friend may have a different antenna, and definitely is in a different location, so the tests at his house only proves that your TV's are working and correctly set (OTA vs cable, for instance).

You might want to post a Fool report for HIS location, at the elevation above ground of HIS antenna, using the map function to precisely place it, for comparison sake.

But at the end of the day, the amp is the only thing you haven't replaced (unless I missed it in there somewhere), and it's the most likely thing to fail 'hard', and your signals are marginal to start with, so I'd consider that as your next move. And if you do that, get a recommendation here for an amp, as I have learned that a poor amp can do as much damage to the signal by adding noise as it does good by boosting strength. If your going to spend money, spend it well.