here are some example test results of a working cable, if you get very different results please post them:

Code:
Examining interface COM3...
USB Serial Port - FTDI
Serial# A50285BIA
VID/PID: 403/6001
WARNING! Your FTDI interface is probably counterfeit.  This may not be a real problem, but if you have issues, you may have to try another.
The bus has been silent for two seconds.
Test data: 10 chunks @ 1b
Test latency results: TX=0ms  TX/RX=14ms  RX=14ms
Test data: 12 chunks @ 2b
Test latency results: TX=0ms  TX/RX=15ms  RX=15ms
Test data: 20 chunks @ 3b
Test latency results: TX=0ms  TX/RX=15ms  RX=15ms
Test data: 10 chunks @ 32b
Test latency results: TX=0ms  TX/RX=15ms  RX=47ms
Test data: 10 chunks @ 64b
Test latency results: TX=0ms  TX/RX=15ms  RX=79ms
Test data: 8 chunks @ 150b
Test latency results: TX=74ms  TX/RX=0ms  RX=116ms
Test data: 4 chunks @ 400b
Test latency results: TX=386ms  TX/RX=0ms  RX=108ms
Test data: 1 chunks @ 1000b
Test latency results: TX=1088ms  TX/RX=0ms  RX=141ms
All tests OK.  This interface should be safe to use.  No warranty.