I'm assuming we have pretty similar proportions when I say the following:
I wouldn't say you MUST be wide on squats, but it really helped me a lot. If you're eating a lot and still not getting bigger then you probably have too much volume in your workouts. You're a big guy already and it takes a lot of calories to maintain that. If you burn too many during a workout and THE RUNS the military is making you do, you'll never gain. When you're trying to get big Army Running = bad, Army Rucking = awesome.
Not sure how much you PT, but less is more when you're trying to get bigger.
Are you using double-overhand grips when you dead? Try going under/over and you'll probably be able to ditch the straps. If you start chasing a high 1RM you might benefit immensly. Maybe start sumo? I notice when I pull sumo my lower back takes less of a beating, and my hammies/glutes work a lot harder. This allows me to lift more weight and really get my upper back busy.
I know I never gained anything but soreness out of high rep deads. Once I started sumo and low repping I went from trouble with 365 to 555 in about two years. Not huge numbers by any means, but way better than where I was.
Totally agree with GOMAD, it is a godsend for tall guys. You have to win the calorie fight to win mass. Run less, eat mOAR!