[Web proxy rules] and [Traffic Shaping]

I’m have been playing around with both [Web Proxy] rules and [Firewall Rules]. By setting this set of rules on [Web Proxy] rules:

After restarting squid, this rules (currently disabled) got me a high download rate for the IT-PCs, we talked about his here. However, when any terminals member of IT-PC use the proxy, other terminals not member of this group get a very slow connection, I believe this has something to do with [Traffic Shaping] so, how can I change [Traffic Shaping] on [Web Proxy] rules?