Are you doing any group riding? Intervals are great, but riding with people faster than you will also help with speed. I spent all summer riding with kids (literally, interns and the 17 year old son of a friend) and trying to keep up with them made me a lot faster! Like 4 miles an hour faster. Find a group of people, 2-3, that you can ride with who will truly push you (and be there to pick you up!) And ride with them if your DH won't. I push my DH, as his pride won't let him be beat by a girl! I do intervals as well, and really focus on form as well as speed/heart rate, but when alone, we can slack - not when with other people! It helped me tremendously.