Having raced bicycles for many years, everything from track sprints to 80 mile road races to 3 hour mountain bike races, I may have a few tips that might help, Joe.
The one thing that helped me perform on the day of an event is that one must hydrate and feed the day BEFORE the event. This particularly applies to endurance events. The day before, basically walk around with a gallon jug of water in your hand. Also make sure you feed well, starting with a good 40/40/20 breakfast and continue all 3 meals that day as healthy, balanced, and plentiful.
The day of the event food-wise you will supply your body with "catalyst" calories to help burn your energy stores. If you wait to feed until the day of, particularly with an 8am key time, you will be in trouble. Day of the enduro, breakfast is a must. So is feeding some at 1 hour minimum, 2 hour maximum intervals. I carry Clif bars and may eat a half or a whole one depending on where we are in the ride. Again, this is catalyst food to keep your body working correctly to burn its energy stores.
The second comment I'll add has to do with the duration of the training. The only way I was able to be competitive in the closing minutes of an endurance event was to have trained LONGER than the duration of the competition. With today's busy work schedules this is a toughy. Unfortunately, if you don't have at least one really long workout that exceeds the duration of your competition, you will hit a wall about 15-20% past the duration of your average workout. Your overall fitness level may allow you to work past this wall, but it will be there.
Keeping in mind we do this for fun, if you can't get in the long workouts here is a tip that may help you get thru the events. It sounds simple, but pace yourself. That is, if you bump up against your max heart rate early on in the event, back off!! You will be able to operate during a 3 hour event in the 80-85% no problem, but once you get over 90% you have a finite time you can operate PERIOD. Stay out of the 90% range early on and save it for the end. Otherwise, you will having nothing left for the end.
This last tip is particularly true if you don't train much over 90%. If you don't do intervals in your training, then doing them in the event will fry you quickly. If you have a decent fitness base and are active in your job, then adding intervals to your training will make a HUGE difference in your ability to go hard early in spurts and still have some left at the end.
Lastly, with the heat coming, if you are a desk jocky then try to get out some in the heat of the day if possible during the week and one training session on the weekend. Heat can be quite a shock and basically knock you out.
Good luck in your next one and take care.