RFX-900/1800 very low Tx power in 1800Mhz band

We are trying to transmit from a RFX-1800 / RFX-900 cards. In the 900Mhz
range we get a normal +23 dBm output. However, in the 1800 range, the
output is less than -6dbm. Has anybody else seen this? This is also with
fresh new cards from Ettus. We made the following changes: burned the
eeprom, installed the capacitor and even got rid of the SAW filter. Any
known malfunction that could cause this?