Need running help!

Hi everyone, i am doing this 5 mile mud run in a little less than 3 weeks. 2010 SEABEE MUDRUN | Gulfport, Mississippi 39502 | Saturday, September 18, 2010 @ 8:00 AM
I need some advice on how to work up to being able to run majority of it. On my run tomorrow morning i am going to run for as far as i can until i cant push any further. I want to see what my max running distance is. I will then work up from there. Time is not an issue, its just having the endurance to finish it without stopping(i want to push myself to not to stop). Any advice would be appreciated.