Upload data transfer drop to 0kb constantly

Hi, i have a unusual issue.
FlashFXP start uploading perfectly and seconds later drop down to 0 kb/sec for less than a minute and later continue uploading perfectly.. this CYCLE happen every 2 mins (aprox, not exactly) always without disconnect from the server. and in differents servers not only one.

Im using Windows Vista, default flashfxp options. and the problem persist even if i run the soft with compatibility to XP or without firewall (kaspersky)

Thanks for your support.

Sounds like some kinda of QoS is running, hmm.

Does/did this happen under windows xp? Does this happen on other pcs running Vista? Does this occur if your av/fw and any other network traffic monitoring/manipulation software is disabled or uninstalled? Are you using a gateway or router with qos, spi firewall, connection filtering, or etc enable?