Hi, I suffer from an identical problem, weight gain has always been a problem for me even although until recently I did very little excersise, in my case it is related to high motabalism, lack of diet control and also lack of commitment. Recently I talked to a few freinds of mine who are big into nutrition and they recommended a weight gainer specifically one made by CNP, its called Pro Mass(they have a good web site with a good forum). I have had a great deal of success using this, managing to put on a much as 10 pounds in less that 3 weeks, this was not just down to the weight gainer I had to up my normal food intake as well. I aim for about 3000 a day as well but I regularly dont achieve this which dissappoints me! I have found that to maintain weight I need to take in between 2000 and 2500 a day.
One thing I have found is that my body weight can change greatly from day to day, even hour to hour, all food types(fat, protiens, carbs,WATER) are absorbed by the body at different rates, I weight my self far to often but really only pay attention to my weight on a Tuesday morning and this is what I use to guage my gains.
Another thing I have found and this has been the best hidden gain, is the increase in energy and as a result happiness and wellbeing, I dont want to make a big deal of it cause its a bit girly, but the change in me has been noticeable.
I know how tough it is, in many ways I believe it to be more difficult to put on than to take off if you are a hard gainer.
Best of luck
PV