Informix 7 slow over WAN yet fast over LAN

All,
My Informix 7 Server peformance on the Local Area Network is very acceptable,
when connecting a new site using 2 Mbps, client experience was lousy, it took
minutes to open simple forms, which took 1 or 2 seconds on the LAN. We
thought that bandwidth is not enough, so we monitored the WAN port and
utilization did not exceed 30%.
When Monitoring the traffic we found too many PSH,ACK and ACKs going between
Server and Client.
Did anybody see this before ? Can anybody help ?
Regards
Walid
.