Thanks so much, both of y'all.
Something is definitely wrong. I took the amplifier completely out of the equation, and installed a new matching transformer to the antenna. I used a continuous run of rg6 from the transformer to a borrowed TV with a signal strength meter.
It fluctuates WILDLY from 0 strength to around 60 (out of 100). After I installed the new matching transformer, it made the situation worse.
I will try and go get a new roll of rg6, as I used the old run because I didn't have any more. So now it looks like the problem is bad/corroded connections on the antenna itself, or bad cable.
I feel like I'm making progress, although my picture/signal is worse at the moment, haha.
Will report back after I replace the coax cable
