I have an internal V.34 modem that appears to perform very poorly.  I get a
lot of CRC errors when using programs such as Telix connecting to a BBS. 
This condition started at the same time as I upgraded my motherboard from
386 to 486 but at the same time the local Water Board dug up my road and of
course managed to cut some telephone cables - not mine fortunately.   My
throughput has dropped on a V32.bis, LAP-M connection to about 1100 to 1250
cps whereas previously it had consistently been above 1500 cps.   It has a
16550A UART.   I always use hardware flow control (CTS or DTR) & in
Telix for DOS turn on drop CTS during a disk write.
I have tried a Maestro 144FM which is a slight improvement (external LEDs
are sadly missed on internal modems).   As I always get a V42 (LAP-M) error
correction on connect I would have thought any line errors would be
detected and corrected transparently to the software downloading the files
Zmodem always used, accasionally ASCII text transfer.
I feel it should not be the line that has degraded but either resides in
the internal modem or my own lack of knowledge in setting these infernal
devices up.
Any clues?

--- Maximus/2 3.01