Let's see if I can summarize your current configuration.
Your gateway has no RTC chip on it. You have removed the ceramic resonator and instead wired it to the RFM69 crystal.
Your node does have an RTC chip on it (the am1805). The moteino still uses the resonator it came with. What about the RTC? Is it using a crystal or resonator? On Tom's thread about the am1805, he seemed to imply it was needed. The way I read the datasheet, an external clock/resonator isn't needed (though accuracy suffers). However, I presume you aren't using an external clock/resonator for your RTC, and so it's also more motivation to sync with the gateway.
Right so far?
If the above is right, then when I wrote reply #8 above, I was mistakenly thinking that your Moteino node, like the gateway, is also using its RFM69's crystal. I'm not far enough in my reading of the atmega328p's datasheet to know if there's a way to "trim" the node's atmega328p clock (it might be nice if there were) to get it to sync with the gateway atmega328p clock... but I'm guessing not. Even so, I was thinking that with that configuration (i.e. the node also running from its own RFM69's crystal and the gateway running from its RFM69 crystal), it maybe would be easy to compare the node's RFM69's crystal speed against the gateway's RFM69's crystal speed and from that deduce a proper frequency offset to align the node's RFM69's radio frequency with the gateway RFM69's radio frequency. [That's because, as I understand it, the radio frequency is achieved by multiplying the 32Mhz frequency by a constant and then adding/subtracting an offset to arrive at the actual radio frequency.] Anyhow, there may be other/better ways to do it, but that was the notion I was assuming when I wrote reply#8.
[The TL;DR for the benefit of anyone else reading this: an accurate syncing of the radio frequencies would be useful because the RFM69 crystals are maybe 10ppm (the HopeRF datasheet leaves out that vital information, but another thread on this forum tries to narrow down what it probably is), and aren't temperature compensated, and that by itself isn't good enough to ensure that some of the narrower Tx and Rx frequency bands even overlap, let alone are adequately aligned. In theory someone could make a hardware module similar to the RFM69 but which uses an accurate TCXO, but, AFAIK, no one does at the moment, so we have to work around the inaccuracy of the given hardware if we want to utilize the SX1231h's full potential. ]