serious isa performance problem

[alpha88]

I'm having a performance problem with isa server 2004. Basically what I have is a retransmission problem the strange thing is I only get retransmissions if I use http basically web surfing or downloading anything, but if I use ftp I get know retransmissions at all. I downloaded a large file via ftp no retransmissions than I downloaded a large file via http the retransmissions were out of this world. I have mainly been using netstat -s and netmon to physically see the retransmission problem. Does anyone here have any ideas because I'm at a lost. I thought it was a cabling problem or bad switch changed all thise out and the problem still did not go away. Also isa 2004 is the only firewall that does this. I've tested sonicwalls, linksys, netgear, astaro security link and checkpoint none did this.