low serial speed & GPRS

I've set up a gprs + OpenVPN connection on an embedded box, but due to the
serial line limitations, I'm able to speed it up only to 9600.

[BOX] <----serial line 9600bps ----> [GPRS modem] <---- GPRS net(>9600)

In this scenario the bottleneck seems to be the serial line speed, not the GPRS
net, but the worst thing is that it's not just a matter of speed but it looks
like many packets get lost.
Can I work with such low speed serial speeds? What am I missing here?

TIA,
J.