The difference between your first TV Fool report and the latest is quite significant.
The first report showed strong signal levels for more than two dozen stations. Your updated TVFR shows most of those signals weaker, blocked by terrain. I'm still not convinced you should need an amplifier. Your original description mentions only one tuner connected... so there should be no splitters. The Winegard HD7697P should be able to receive more than enough signal to power one or to sets with no problem.
(An overloaded amplifier is one that has more signal power fed into it than it can handle. The 8700 is designed for use in locations where the combined power of all the signals is moderate to weak. There are amplifiers designed to handle stronger signals but you are describing a situation where no amplifier should be needed. Rather than dwell on the amplifier, let's work toward understanding why a perfectly capable antenna was not able to produce a long list of usable signals to begin with.)
A big unknown is the effect of the attic construction. Some attics are quite acceptable locations for an antenna installation... but some attics block, reflect or interfere with TV signals to the point that reliable reception isn't possible. In some cases, the problem affects just one or a few channels.
JC's suggestion to run a 'test' coax directly from the antenna to the TV is the most logical next step. If reception improves, it suggests a problem with the original coax and/or the preamp.
I would suggest as a second test (if needed), test the antenna outside, with a clear view to the west, at or above the height it is now. Use no amplifier, just the single test coax. (Quad-shield won't hurt but it won't provide any benefit either.)
Sometimes it's easy to confuse the front and rear of an antenna. Your description of the symptoms makes me wonder if your antenna is aimed east rather than west. That could explain why you saw so few stations before adding the amplifier. Just to be sure, here is a link regarding aiming antennas of various types:
www.kyes.com/antenna/pointing/pointing.html The closest match to your antenna is the 'all band UHF-VHF-FM'.