That is a very impressive CV of progress, Ballesteros.
Your weight loss alone is, theoretically anyway, good for over a minute off your mile pace. I am guessing you did some serious dieting. Your exercise regimen alone would not normally account for a 28 pound weight loss.
Do 10 x 1000m @ 4 minutes every week. Start with a 2 minute recovery then gradually knock 5 seconds off the recovery till you reach 1 minute. If you can do that then no probs.
Also, if you could get your weight down a bit it would help a lot. You don't say how tall you are but if you're under 6 feet then you're a bit overweight for a sub 40 runner. I am 6 feet and a bit and weigh 11 stone 12 and could still stand to lose a bit of weight.