Calls are being dropped after 5 minutes. The provider is sending a mid call ack alive request. They never see our ack alive back. Anyone run into this? Maybe the router/firewall is closing the port after the call is up for a certain time?

2 thing to try:

Port forward the sip port to the MP card.

Or you can turn on alive notify to send an options message every x seconds (anything less then 5 minutes should work, i usually do 30 or 60 seconds) this keeps a connection alive in the router/firewall NAT table

I had this issue with another carrier last week and had to turn on PRACK support in the SIP carrier options and it cleared it up.