1.007??? What the %&*#
That's totally unexpected considering your recipe and process. Some of your measurements have to be off. Either your thermometer or your hydrometer. I know you previously stated that you have calibrated them, but this is very odd. I would not expect a final gravity that low.
What yeast did you use?
I can certainly understand your frustration.
I'm still pretty confident that my thermometers are properly calibrated. But I just ordered a thermapen in hopes of putting that issue to rest (and because I've always wanted one!).
Although my mash program indicates a beta step time of 25 minutes, the mash sat at beta temps for much longer than that. I pulled the decoction at 25 minutes and then rested the decoction for 15 minutes at 158 before boiling it for 30 minutes. So the mash really sat at beta temps for over an hour. Based on some of the responses I've gotten on this issue, I'm reasonably confident at this point that the high attenuation is due to the prolonged beta rest.
Going forward, I may try pulling the decoction at mash in, as Tygo suggested, but then I think I risk having the main mash temperature drop significantly due to the lack of thermal mass. Also, I just don't know if I could get the rested and boiled decoction back into the mash tun within 20-30 minutes, which is my typical beta rest time.
So, I think what I'll most likely do is either: (1) step mash using only using infusions since I can control the step times much more that way; or (2) accept the limitations of my cooler mash tun system and avoid step mashing. Under either scenario, I can still do a decoction to hit mash out temps if I want.