Faxing with T.38

I am not sure if anyone can help or has any advise, but thouhgt I would ask. I am using asterisk on a FreePBX distro I am trying to get t.38 faxing working with my carrier, but having no success with ATA gateways. The carrier supports T.38 and so does the ATA gateway.
When debugging I see that T.38 is agreed on, but the ATA gateway does not ever send anything. The ATA gateway is a grandstream 4004 FXS gateway.
I can not send or receive faxes with T.38. If I change to pass-thru it works, but only 70% of the time. The freepbx guys say that there is nothing to change on the asterisk or freepbx for T.38 and I am waisting my time. They are pretty sharp and I beleive them, but I cant help, but think that something might be done to at least get the T.38 to negotiate, if it fails after that I can come to terms with that.
Is there anyting from an Asterisk point of view that can be changed or verified?
Thanks in advance.