It might be useful to get the post call diagnostics -
AT#UD
is the command, and you may need a decoder to have the results mean anything - see
www.modemsite.com/56k/diag.asp (Connexant)

It might be ever better if you have return privleges on the modems (it's probably been 4 or more yrs since anyone manufactured a 2949C) to return them and go with a different / current modem - (I'd go with an Agere-based softmodem).

It does look like, at least on the connection you show, the receive data rate is poor (19.2k vs 31.2k up), and noisy. So there's probably a fair amount of error correction going on in the modem; it could be that Procomm, also using a software error control download protocol detects an error before the modem has finished its own retransmission/correction.
So, I would suggest trying these things:
Use a non-error correcting download protocol and let the modems do the error correction;
or, disable error correction on the modem (although this may result in problems before you start the download) and use an error correcting download protocol with Procomm;
and/or/plus try to speed limit the TX rate (and if that doesn't work, the RX rate as well) - www.modemsite.com/56k/x2-linklimit.asp -
I'd first check multiple connections to see what the TX/RX connect rates are, and if RX is always 19.2 or so and TX is much higher, limit TX to about the same rate as RX; if that doesn't help, you could try limiting the modem protocol to V.32 or V.32bis - www.modemsite.com/56k/ms.asp or try even lower RX rates/