I've always had a hard time gaining weight.
5'10-5'11 and have usually been about 150. Once I hit 175 -185 or so, but it wasn't all muscle either.
I think the biggest thing is one plan doesn't fit all.
I can drink beer as much as I want and never gain weight. I think it messes with my digestive system. I actually lose weight.
Currently, eating lots of protein and carbs (pasta bread) in medium portions. I try to eat 4 times a day.
Hardly any sugar, cut back on the beer and have been gaining. I'm shooting for 16-17in (but toned arms) in arms and keeping my waist at or under 32. It's never been more than that, so I don't see a problem there.
Legs are far behind due to injuries, but are starting to look better.
Currently I'd say I need another 25 pounds or so with only adding about 2% body fat.
Definitely need to start working on cardio, but I'm horrible at it at don't like most cardio things. Swimming would be ok, walking (bad knees) is ok but not really cardio. Running, nope. I have an elliptical and it's ok, but I needed more leg strength from squats and such to get much cardio on it.
Keep up the good fight guys. Figure out what works for you and do that.