Serial port slow on Linux dosemu

I've scanned the archives and tried everything I have read but my serial 
ports are still very slow. I'm running some CableEye software and 
connected to a cable tester via ttyS0. I've migrated an old p3 box to a 
newer (still old but) Dual P4 2.2GZ processor. Everything works but the 
serial port is too slow. The old p3 would test a cable in a second. Now 
in the emulator it takes 8 seconds to test the same cable.

I have tried these 2 combos with no luck

$_ports = " device /dev/null range 0x3f8 0x3ff fast"
# $_com1 = "/dev/ttyS0"

and

#$_ports = " device /dev/null range 0x3f8 0x3ff fast"
$_com1 = "/dev/ttyS0"

They act the same. How can I get this thing to sing?

Thanks in advance
Mark