Four of the LA stations will switch their digital channel from UHF to their current upper VHF analog channel next February 17: WABC-DT 7, KCAL-DT 9, KTTV-DT Fox 11, KCOP-DT My 13. All of those stations with a digital channel above 51 will move to the upper VHF or lower UHF. The UHF channels 52 to 69 are being taken away from TV broadcasting. That should help digital reception at places like Temecula Valley. 

I use a CM4228 at about 40 miles and get perfect reception. I even get 
better VHF reception with it than I did with my actual vhf antenna by 
about 15% more signal strength. The 4228 is not near as critical on 
direction as yagi style antennas are. Even the slightest movement of the 
yagi antenna I had would drop out channels. That may be what's happening 
with you. I'd try a CM 4228. I've heard of people using it at 100+ miles 
with success. Not sure how well it will work on VHF at 75 miles, but it 
works great at 40+. It even picked up lower UHF (5) better than the real 
vhf antenna, but couldn't get 2 at all.

Other responders have made good points about antennas, so I'll limit
mine to amplifiers. You say on your site that you are using a Radio
Shack 15-2507 mast-mounted amplifier and ask if the Channel Master
7775 might give better results. Probably, but not for the reason you
may think.

Many people make the mistake of selecting an amplifier by its gain,
assuming a higher gain will give better reception. Certainly the
receiver needs a minimum level of signal to work with, but any
amplifier can give it that. What's far more important is the
signal-to-noise ratio (SNR).

Noise is everywhere; it rides in on the antenna, it may enter on the
cable or other devices on the path to the TV, and it is generated by
every electronic device (even resistance) that the signal passes
through. An antenna preamplifier cannot improve the SNR it gets from
the antenna. In fact, it will always make it worse. Its job is to
amplify the signal AND noise so that they are both much higher than
any noise that may get added in the cable run, and to add as little
noise of its own as possible.

Noise figure is the measure of the amount of noise an amplifier adds
to the signal. It is measured in dB and lower is better. Good
amplifiers are around 2-3 dB, like the Channel Master you're
considering. Poor ones generally don't list the noise figure. I
notice the link to the R-S amp doesn't mention it.

Post to alt.tv.tech.hdtv your observation/opinion, I will post it here!