faster backstroke

Not sure if this goes in this forum or not, but I could really use some help on this. I finally have got my freestyle times to be below 40 sec. consistenly for 50 yds (i know it's slow but it's the fastest I've ever been personally), and now I would like my backstroke times to come down. I feel like I've tried everything I know to make them faster and I'm feeling kind of stuck. I do some interval training but they still seem to be in the mid-40's for 50 yds. I think I roll enough (I show my shoulder on every stroke) and my kick is decent, but when I kick hard, I feel like I sink. I've tried everything that I can think of and all kinds of combinations of kicking and arm speed to get myself to go faster and no matter what I do, I still can't get my times to come down. So anyway, now that I'm done complaining (sorry)I was wondering if anyone had any tips to help me out? Thanx a bunch!! ~Kyra