I've told this story before, but when I got weighed at K2 Aviation in Talkeetna, the kid with the clipboard said, "Geez mister, you're the biggest guy we've had come through here." With my gear, I topped out at a little over 400 lbs.
I'm 6' 2" and I weigh 240 and have no trouble in the mountains (so far). My knees will hate me some day, so I try and lose weight for that reason alone, but it's not easy. Course, I drink and smoke in the mountains too, but that doesn't seem to hurt too much (pick your vices). I dropped 25 pounds on a 3 week Denali trip, but put them back on within a month when I got back home.
Sounds like you are very active and if you're going to push yourself then I would focus on core stuff. Cut back on the bench and keep it up with the squat. Very few people actually do the deadlift correctly, so I would advise against that as well. Try yoga, core strengthening (not just the front, back too!), legs, and get out more with a heavy pack. The best training for being in the mountains is to get in the mountains. And Marathons don't have much correlation with mountain performance. I've run a few marathons as well and they do as much good as they do harm. Great cardio and they focus you to get into a routine, but pushing a pack up somthing vertical is another group of muscles. Lot's of marathoners turn around on big mountain climbs cause they cant take the pack, the sled, the altitude, leg/hip pain, etc.
Diet, that's a whole nother ballgame. I saw a nutritionist the other day and for $200 he opened my eyes! It was illuminating. Maybe give that a shot as well.