My 2 cents worth about improving on the hills, which goes along with what other people have posted is:
1) get a heart rate monitor and shoot for the lower zones, fat burning and aerobic, not the higher zones -- lactate threshold and anaerobic,
2) watch your cadence, shoot for 90-100 rpm on the flat and 60+ rpm on the hills,
3) speed on the hills is not important, it is your cadence and heart rate, if your heart rate is maxing out and your cadence is nil on the lowest gear, you need a bike that gears down further so you can crawl up while turning at a decent rpm and heart rate (will get high, but avoid anaerobic).
If you are not losing weight, and you want to, you are going to have to count and limit calories. 30-50 miles per day is a lot of riding and doesn't allow much recovery; at 30 miles you probably don't exhaust your glycogen stores, but at 50 miles you probably do and then 'have no strength left'. 30 miles is roughly the 'bonk point' if you don't eat while riding.
I am a very similar case to you. I am 5'9" and was 180lbs 4 months ago, now, I am 155 lbs as of the last 2 weeks. (I have been on SSRI for about 4 years. I was 155 lbs give or take 5 when I went on medication. The last 3 years I have been +175 lbs.) I have been eating 1750 calories a day and riding about 100-125 miles per week, 4-5 rides, 15-30 miles per ride, one day hills, rest of days flat. Hills here are about 1 mile long and pitched where I can coast down at about 30-35 mph. The first two weeks of 1750 calories was hell, but I got used to it. I eat plenty of fresh salads and fresh and frozen vegetables. And, I get plenty of sleep (8-9 hours). I also carefully watch my caffeine intake. 2 cups coffee in the morning and no other caffeine works best for me and I consider it to be the proper buffer for my medication. The riding is also great for my mental health and I just love to get out there!
As I mentioned, my diet tricks include:
Nice big salads
Add half a bag of frozen vegetables to a Lean Cuisine Meal
Drink flavored carbonated water (no caffeine or sugar)
Regularly Eat baked potatoes (with salsa instead of sour cream or butter)
Avoid Fast Food
Best of Luck!!