Ok.
Start now, and in 8-12 weeks you'll be laughing at the guys who are panting and gasping for air at the finish.
1) Switch to HIIT cardio 3 days per week. You need to get your body accustomed to working at a greater intensity.
2) Start doing jump rope. The deceleration on 52 sprints is going to be the killer. The jump rope will condition your tendons and ligaments, which are going to take a beating. Train them properly, and you won't notice it at all...you'll be conditioned.
Start with 5 minutes and add 30 seconds each week until you're up to 10.
3) Do a Google search on "Tabata protocol", or start with this article here:
http://www.achieve-fitness.com/ideal.htm It is a 4 minute drill. Start doing these 3 times per week. They are brutal, but effective. You can do them on bikes, an elliptical, with bodyweight squats, with squat-thrusts, etc. They WILL increase your cardiovascular conditioning quite quickly. If you're going to run, though, a treadmill won't work. It just doesn't change speeds fast enough, which is why I recommend all the other possibilities. Squat thrusts will probably be the most difficult, if done at the intensity recommended. Since yours is a 6-minute test, I would add 15 seconds each week until you were at 6 1/2 minutes.
4) Sprinting on a basketball court could be done twice per week. Unless you have access to an NBA court, the total distance is 84 feet. Instead of doing the whole thing, go from one end to the other side's free throw line, which will be 65 feet. For decelaration purposes, I would suggest that you decelerate and not allow yourself to go past the free throw line. That will best simulate having about 5-10 feet to stop. The deceleration portion depends on your testing environment and can be adjusted as needed. Start with 4 minutes and work your way up to 6.5, just like with the Tabatas.
5) Don't lift slow. Ever. The
amount of weight may force you to move slowly, but don't lift "slow" on purpose. Think "fast". Lifting slowly is one of the most ignorant things ever to hit the athletic realm...forgive my bluntness.
Always "intend" to lift fast. Always.