Unfortunately, adaptation to altitude is a few weeks of process, as what happens is the body kicks up production of red blood cells, and that's not an instant thing. As noted in the comments, getting there a few days ahead will help.
Also, be very aware of hydration, and make sure that in the days leading up and especially during the event, you are getting a lot of water, and avoiding high doses of caffeine (If you are a regular consumer of drinks such as monster, etc). Caffeine in low doses is not a diuretic, but 600mg+ it can have a diuretic effect, and with the consumption of multiple energy drinks you can hit that level. You dehydrate faster at altitude than you do at lower elevations, so you will probably need more water than you think you do.
Be aware of symptoms such as headaches, vomiting, dizziness and somewhat sudden fatigue, as these are signs of altitude sickness. Most people can ascend to 8000 feet without too many problems, but you will also be doing the tough mudder which is a pretty rigorous event. Don't be afraid to stop and breathe for a bit if you start getting dizzy and nauseous.