Hi Bro
I don't think this is a FWSM issue, but then again you never know :-) There could be few possibilities,
a) Is there QOS / MFP configured in your FWSM context?
b) Is your FWSM overloaded e.g. CPU/Memory Utilization?
c) How big are these uploaded files (>100Mb)? This is because the FWSM backplane is 5.5Gbps.
Warm regards,
Ramraj Sivagnanam Sivajanam