The day/night cycle you are seeing is caused by an effect known as atmospheric ducting. Almost all of your stations are so far away that the Earth's curvature is getting in the way, and the transmitters end up below the horizon for you.
Here's a cross-section view of KTWU as an example. In this view, transmitter is on the left, and your location is on the right.
Note that the signals can only reach you by either diffracting over the tops of hills, bouncing off the upper atmosphere (E-skip), or bending through the lower atmosphere (ducting).
Diffracted signal is the most "direct" path between the transmitter and your antenna. Due to your distance and the terrain, the diffracted signal is very weak for most of your stations. This kind of signal is usually pretty stable throughout the day.
E-skip depends on ionization effects in the upper atmosphere (e.g., might be caused by meteor showers, solar flares, and other events) that allow radio signals to "bounce" and reach places far beyond the usual coverage area of a transmitter. These kinds of events occur sporadically, but when they do occur, it can significantly increase the received signal strength at great distances.
Atmospheric ducting is caused by a temperature inversion in the lower atmosphere (warm air near the ground, cold air above it). This turns the lower atmosphere into a kind of lens or prism that causes radio waves to bend back toward the Earth (i.e., follow the curvature of the Earth) a bit. This kind of effect primarily benefits people that are roughly 60 to 90 miles away from a transmitter (far enough to be below the horizon, yet still close enough to see a noticeable increase in signal strength). The increase in signal strength can be quite strong in the right weather conditions. This effect is usually strongest in the evening/night because the upper atmosphere cools after sunset, but the ground (gathering heat all day) keeps the lower atmosphere warm.
The bottom line here is that your main signals are pretty weak because the transmitters are so far away. Your antenna setup is probably just shy of being able to pick up the main signal during the day. You are reaching for channels that are generally considered to be very hard to get ("gray" zone in your TV Fool report).
It sounds like a few of your stations are getting enough of a boost from atmospheric ducting so that you can see them during the night.
If you want to get the channels all day long, then you need to improve your antenna reception so that it no longer relies on ducting to pull in enough signal.
The CM 7777 is already a decent amp. The Winegard amps have very similar specs, so my feeling is that switching to an AP-8275 amp won't make that much of a difference.
If you want to see an improvement, you need to do one or both of the following:
1) Increase your antenna gain.
2) Lower your pre-amp noise figure.
Switching to some higher gain antennas (like the Winegard HD8200U) might give you a few dB of improvement. Using separate UHF and VHF antennas (best of each kind) might also do a little better than a "combo" antenna.
If that's still not enough, you can gang multiple (identical) antennas together for even greater gain. Expect about a 2-3 dB improvement each time you double the number of antennas you have.
The Channel Master and Winegard amps have Noise Figures of around 2.8-3.0 dB. There are some pre-amps available with Noise Figures of around 1.0 dB or less. This can improve your net signal margin by roughly 2 dB.
Hope this helps.