I lost about 10 pounds a month on 40-60 carbs a day. I think it helped that I had only 40 pounds to lose, I had previously been very active for years, and I didn't have any "blow out days."
Also, I suspect you are a man...which means you lose more easily and don't have to deal with hormone fluctuations the way women do.
If you haven't messed up your metabolism with a lot of yo-yo dieting, I think you get the same kind of dramatic results. At least I found mine dramatic!
It sounds like you are doing everything right. Personally, I never moved up the carb ladder that much, I still stay on 40-60 which is where I started. Your body just might be headed for its happy place.
Also, it's normal for things to slow down as you get closer to goal. I've lost 3 pounds in the last 2 months.