Weak signal reception
He's right...
Get the best antenna, high, in the clear line-of-sight path to the station, good preamp and coax.
Now comes the fine-tuning:
1. The preamp must be at the antenna, with as little loss between the antenna connection and preamp as possible. Even 1/2 dB improvement helps!
2. Your preamp at 3.5/4 dB noise is not very quiet. A Channelmaster 7777 is 2.8 dB (VHF)/2.0dB (UHF) NF. If a bigger antenna is not an option, and stacking isn't either, then try a quieter preamp such as the one I mention here.
There is a 0.4 dB preamp out there, but it's over $300! Some people use one if even towers and stacking don't get it in.
3. Minimize the line loss. With a good preamp, this won't be much of an issue, but every little bit helps.
4. Optimize antennas for each difficult channel, such as build that very high gain Yagi for the tough channel, using its own preamp
5. Find the "hot spot(s)" for the difficult channel(s) (locaton/height) and position/aim each antenna to get the best reception possible.
6. You can go to serious extremes, choose your efforts wisely.
7. Antennas and preamps designed for a single channel are used to obtain the last bit of performance avalable.
8. The lowest practical receivable signal level at UHF with hard work is around -106 dBm, isotropic. Extreme antennas might get to -110 dBm. VHF is somewhat thigher due to man-made noise.
9. Refer to tvfool.com for a guide as to signal strengths. Antennaweb is not as accurate.