If you are overweight and good at hills then when you lose that weight and get down to a race weight you will be killer at hills because you will have an excellent power to weight ratio. Usually to race well and actually enjoy yourself you need a minimum of 8 hours a week training. So that could be about 125 miles a week. 50 miles a week is probably not enough depending on your natural ability. Intervals help develop the power you need to stay with the field on attacks or go with breaks and such but if you lost it in the 3rd lap after slowing drifting back then I think you just need more miles in your legs. You need a really good base before you start interval training. About 1K miles is what I was tought to be a good base. There are some pretty good books out there that can help you develop a training program. You can search this forum for some good titles.