You problem is pretty simple.
You now have both UHF and VHF signals and your antenna is a poor performer.
You UHF range when new was only 35 miles.
• Range Designation: Near Fringe
• UHF: 35 Miles
• VHF/FM: 50 Miles
• Length: 94 1/4"
The problem is - even with a TV fool report is that you have to take into account the area in which you live.
A general Zip Code does no good for estimates because the only thing that the TV fool report shows is the general area of the transmitter antenna and the general distance from the transmitter to your antenna.
You have to take into account if there is any trees near your antenna, if there is any buildings near you that are 4 or more stories high. If there is any hills between you and the transmitter. A lot of factors like you said including airplanes and bird migrations and swarms of bugs that can all affect your signal.
Not go get on my soap box and preach, but UHF is line of sight transmission.
If you put a UHF transmitter on a tower 1000 feet above average terrain - not above sea level.
And if you put your antenna 1000 feet above average terrain, you should get a signal.
Since you are in the fringe, you know that you are going to need a good antenna and a good location to put it in.
Basically in the past when a person did not want to do a side mount on the side of their house they traditionally put their antenna on the chimney. Chimney mounts were ok for VHF. But there are several factors that comes into play for UHF that destroys your UHF signal.
A piece of flashing 6 inches wide can block your signal, water on the roof can reflect your signal away from your antenna. Even water under your shingles and moisture in your plywood can reflect the signal away from your antenna.
Basically you are going to have to walk your antenna around the roof until you find a suitable place to put it where your reception will be best.
http://www.hdtvprimer.com/ANTENNAS/siting.htmlI am not going to attack your antenna, but what I will say will shock you.
There is always a off chance that your antenna transformer - if you are using 75 ohm cable, is bad.
In order to receive UHF signals, you are going to have to buy a good pre amplifier and a transformer that does not fall apart after a few months or even a year or two.
My advice would be for you to use a Wiengard 8200U antenna because it has the highest gain for both UHF and VHF. I would also advise that you use a Winegard AP8780 UHF VHF Pre-Amplifier ChromStar 2000 due to the fact that you don't want to over power your receiver.
That amplifier will compensate for your signal loss in your wire and splitters between the antenna and the television.
I would also advise that you use Quad Shield cable due to it's lower loss at X frequency and it's better shielding than regular RG 6 wire.
That set up should get you a 50 mile range.
A Winegard AP 8275 would probably boost it up to about 70 miles UHF.
The question is how much do you want to spend and how much do you want to receive?