JasonC8301- Hey, Jason. I've followed your posts for ages and found them very informative. I'm over twice your age, but I had your "problem" for years and still have a fast metabolism. Though your "problem" sounds pretty good- 165 at 5' 6" with a 29" waist isn't shabby!
My $.02: it sounds like you REALLY loose size when the Corps has you on their diet while doing intense PT. Now that you're out of boot camp and might have a bit more control over what you do/eat, I'd first stop running all those miles if you can. I've cut my cardio down to short, but VERY intense (as in "think you're gonna die" during the tough intervals) sessions, maybe 4 a week max. My cardiovascular fitness is MUCH BETTER for this change, BTW. On your workouts, could you do them in a different sort of split so you only work one major muscle group per workout and thus lift for a shorter time? I'm assuming you're doing low/moderate reps to build functional strength. Two hours sounds very long to me, like what I did back when I had 50 lbs. less muscle. I LOVED marathon lifting sessions, but I didn't build size/strength with them.
When you're doing the corps' PT, you just won't/can't keep your size. I doubt that they would WANT you to! Their view: soldiers don't need to lug around extra muscle (weight), they just need functional strenth and
endurance. As in no benchpresses, but able to do heavy deadlifts and pullups all day.
Oh, for the diet: are you getting 1.5-2 grams of protein per pound of body weight? And twice as many calories in low-glycemic carbs? Getting good fats (fish, nuts, etc.)? You might need to put a little extra thought and planning into it. Tried creatine? It might be good for 5 lbs. and would help your workouts, too.