How To Setup DMZ and IP Passthrough

You have set up Port Forwarding and DMZplus to the same device.  This is likely not going to work correctly.  You want to do either one or the other in the AT&T gateway, not both.

Is 192.168.1.200 the actual device that has the ports open that you want to access from outside, or is it an intervening router?

If the former, port forwarding by itself should be good enough.  If you wish, instead of doing port forwarding, you could effectively forward all ports by setting up DMZplus to the device, but if you do so, then you need to remove any port forwarding you set up.

If the latter, then you need to do DMZplus to 192.168.1.200, then do port forwarding inside 192.168.1.200 to the ultimate device.  I don't think this is what you're doing.

A static address is one that doesn't change.  You've been saying that you have a public static address. AT&T doesn't issue a single public static address.  They issue a public dynamic address.  It changes very rarely, and for most purposes you can treat it as static.  However, when you mention you have a static address, then we're going to go off on static setup, not the standard setup.

Sorry, yes, DMZplus is the name used on some AT&T Gateways (the 2WIRE/PACE line), the other line uses the term IP Passthrough (models NVG*, BGW*).  Same feature.  It's similar to "bridge mode" in that:

1) The target device receives the public IP address from the gateway in response to a DHCP query

2) All traffic from the target device is passed to the Internet without changes (i.e. no NAT/PAT)

3) Unsolicited traffic from the Internet that passes any filters (there are default filters) and does't match a port forwarding or NAT translation is forwarded to the target device without NAT/PAT

At any time during your attempt to set this up have you done a factory reset?  While I've never heard of it on the BGW specifically, many other gateways have had issues that have been corrected by doing a factory reset and clearing out the NVRAM (often this is because a new version of the firmware doesn't deal well with the config data in NVRAM).  Sometimes it happens because the firmware just gets confused with data it wrote when it gets complicated.

There is no account specific information stored in your gateway that wouldn't be replaced automatically during the reload operation when it books back up afterwards.

Brian... 

I am with you 100%, I would switch it back to Spectrum in a heart beat, except, I can't!  So far there isn't anything I like about ATT's Internet nor Direct TV. 

When they sold this to me, I was PROMISED, yes Promised, speeds of 80/80 up/down.  HA! I haven't broken 75 yet, and I hit 75 only once.  Just for {edited for word filter evasion} I just did a speed test. All I get is  23.4 down and 3.10 up. It is 6.42 AM in Los Angeles.  Doing the same speed on the same equipment I used to hit 200/30 (+/- 10) down/up with Spectrum.  
Why can't ATT just give me a modem instead of this stupid router. Why can't I hit the speeds they've promised. Why is the Direct TV interface not intuitive? who designed it? why has ATT peppered all these sales channels all over the place on DTV? I  am paying for a service and yet I am have to claw my way through sales channels to get to my stuff. OH and get this... If I want to watch an older episode of a TV show that I didn't watch a few weeks ago, now all the sudden I have to pay $2.99 for that. I am talking network TV!  A show on CW.  A show I missed to watch/record it 3 weeks ago, and now I have to pay $2.99 to watch it.  I have Showtime, but I can't watch season 8 of Shameless on demand, I have to pay $2.99 per episode! 

I can't wait till this contract is over! 

80/80?  I don't remember there ever being a downstream tier of 80, let alone a symmetric 80.  What speed is actually listed on your account summary?