Maximum https connections from a single ip

[bazz]

I run a corporate chat server which other parties sometimes use, I have just installed a pf sense cluster in front of it but now I'm limited to 129 connection from a single IP (most comapnies use a proxy so all traffic outgoing from the offices go out through the same ip).
Is this a setting within pfsense? (currently running 1.2.3 but can upgrade to 2.0)

Any other things I need to check out?

Chat servers are ubuntu linux with a tailor made application, had this running previously and could do 750 connections easily.

I tried setting up a 1:1 nat but I'm still running in to a max of 129 connections.