We always use sccp for the analog vg'sif it has faxes on it we put these ports on SIP for the T.38 support.
The hold queue thing solved it for US.
Maybe worth a try to put it on sccp.
Paste the running config into a file in flash as a backup and enable sccp
In my case it was because i had a loopback bound to sccp because we usd ospf for ha.
The hold-queue command needs then to be on both lan interfases to handle the burst of registraton messsges on top of all the other traffic.