Remote SSH to RPi on AT&T U-Verse Network

[DaHai8]

I have a RPi running Raspbian at a friends house who is using AT&T U-Verse but no matter what I've tried, I cannot remote SSH into it.
It was previously installed in my home under TWC and worked just fine.

I'm hoping someone here has experience with U-Verse and can't point out where I missed something.

1. SSH service is running and worked fine at my home.
2. The U-Verse Modem is a Pace Plc 3801HGV v 6.11.1.29-enh.ym
3. I've enabled IPv6 as there service is dual-stacked for IPv4 and IPv6 but I can't access it using its Global IPv6 Address and I've verified that my ISP (TWC) is also dual-stacked for IPv6 and IPv4 and that I can access IPv6 only web site hosts.
4. I've tried opening a port forward from 8085 to 22 to the RPI on the U-Verse Modem/Router, but I can't log in with SSH over IPv4
5. The U-Verse Modem, from what I've read, doesn't support UPnP

I know the RPi is actuall running as we can access it locally on my friend's internal network from their PC.

Any ideas?
More questions I can try to answer?
Is there some setting in the U-Verse model that I haven't set?

Thanks!!

[georgeb2014]

I have 4 PIs running in a U-verse network on a newer model Pace 5268AC gateway. 3 of the PIs are temperature/humidity sensors and one is a Flightaware ADS-B Receiver. I can SSH into any them with no problems, EXCEPT, sometimes I had to ping the target Pi to wake up the network. I log into the U-Verse gateway and can see the PIs at their respective IP addresses, and it says they are active. That said, I created cron jobs on each Pi to ping their partners every 5-10 minutes (3 pings on each partner address) and that seemed to make them more responsive to the connections from my Windows system from the Putty ssh client. The 3 PIs running temperature sensors also e-mail out their readings every 4 hours and I was getting intermittent e-mail failures until I started pinging the SMTP e-mail server prior to sending. The Pace gateway is definitely an odd duck for sure. All the gateway timeout looks reasonable for DHCP leases and session timeouts. Before going to U-Verse I was on AT&T's DSL service running a Netgear WNDR3700 router and never had these problems.