Degradation of ATSC signal in summer is normal/expected.
Humidity in the air as well as live/wet leaves on the trees are contributors.
Amplifying is unlikely to help, especially at 8 miles from towers.
I’d say “just wait until late fall and the signal will be fine” but obviously that is not really a solution. You could try pointing the antenna horizontally a couple of degrees away from the troublesome transmitter. This will reduce multipath interference as well as overall signal strength - you may find a “sweet spot” . Additionally try pointing the antenna slightly upwards by a couple degrees - (same idea, try to find a sweet-spot).
I’ve tried all the above antenna pointing stuff in summer, as well as preamplification. Nothing solves the problem reliably for me, but I am about 50 miles from the troublesome xmitters. So my “solution” to this same problem since 2001 has been to subscribe to comcast TV service, without renting any equipment from them (they provide a cablecard for free).