If you used to carry around 110 more pounds than you do now, drinking a gallon of whole milk a day is a horrible, horrible, idea.
GOMAD is great if you're 16, consuming 4000+kcal, or illiterate and can't read up on good nutrition. It's great for convenience. It's great if you're already at your limit of what solid food you can cram down your gullet and you just need some quick calories. It's great if you're a running back at a D1 high school and don't have time, money, will, or opportunity to get something better. But lets be realistic for a moment; a gallon of milk has 2700 kcal and about 130g of protein. Which of these seems like a better option?
Option A: GOMAD. 2700kcal, 130g Protein.
Option B: a pound of steak, half a box of pasta, half a box of sauce. 3000kcal, 400g protein.
One has more protein, creatine, B-vitamins, and slow-digesting carbohydrates (assuming whole wheat pasta). The other has some protein, and a lot of empty calories.
What do you think?
So yeah, count calories and eat a little above maintenance. Eat enough to gain weight, make sure your lifts are going up, and have fun lifting. Don't do GOMAD.