I ran a test that Rich suggested.  Specifically I used an HP signal generator to produce test signals of -50dBm to -90dBm.  The received RSSI at the AX5043 is within 1 - 2dB.  This suggests that the antenna connection, matching circuitry and filter are all working. The signal is getting to the chip as expected.

Tuning the signal up/down does not improve things.  So the chip does seem to be on the right frequency.  I also ran the "test freq" function (after modifying it to work with the AX25 code).  It transmits on the receive frequency, and it seems to be correct within a kHz or so.

So this leaves us, as expected, with some sort of register setup issue.  Given it is worse on 2m than 70cm it is perhaps a bandwidth or frequency acquisition issue.

73

Chris