One passing contemplation here, (Not thought, as that would hurt too much.), would be to see if your AM TX is possible of even going 100% modulation. There's some cheap kits out there that struggle to do 50%, at best. Anyway to put that to an o'scope, or an off-air AM monitor VU meter, to see what a 1kHz test tone does when you vary the audio input level? Then again, just like most modern day CB's, there maybe a limiter in your TX to on purposely keep that level low, in order to boast Part #15 FCC compliance. (OK, that was a couple of contemplations.)