If outdoors, antenna components and accessories do tend to degrade over time, primarily due to the effects of water infiltration into baluns, coax cable, and connectors, corrosion between adjacent metal components and connections, and the potential for electronics to get "zapped"by static discharges (ie, lightning, etc.).
If you replaced a medium gain preamp with a high gain amp and you're feeding that into a distribution amp, the probability of overloading an amp or tuner is very high.
Let's see the corrected link to your TVFool plot so we can get a better idea of what's going on.