[ADTech]

It's the trees, in my opinion.

I've seen situations "out in the woods" with my spectrum analyzer where signals can vary as much as 20-30 dB on some channels (but not others) just by moving the antenna a few feet. On another occasion, I've been within visual line of sight, excluding trees, of a million watt UHF site here in St Louis, and a single big silver maple tree in full leaf would completely wipe out reception of that station when the antenna was behind the tree and the wind was blowing. Moved a hundred feet off to the side and the signal measured as expected on the analyzer.

Best course of action I've found is the combination of the following:

1) Largest UHF antenna feasible for the situation (might call for a Yagi, 4 bay or 8 bay).
2) Mount the antenna as far back from the trees as possible.
3) Mount the antenna as high as possible.
4) Boresight the antenna to the visual horizon at the treetops.
5) Judicious use of a preamplifier to preserve whatever signal might be at the antenna's terminals.

That's it, short of making firewood out of every tree that's confounding your reception, building an extraordinary tower above the trees, or calling United Van Lines.

I would certainly suggest trying the 4-bay UHF antenna. Your odds will be substantially better. Be very flexible on selecting its mounting location and don;t drill any holes until you're satisfied that reception is as desired. If you have VHF channels on your "must have" list, you may well need to address them separately.