6 hrs of Brown-town

Woke up to showers Saturday morning, which can make the South Texas soil stick to your tires like peanut butter to a dogs mouth. Fortunately, they stayed light showers, the wind kicked up and the course was it great condition after the first lap. We started with a LeMans start,the longest I've ever done, it was about a 1/4 mile,hopped on the bike and was off. I was in 4th starting the bike and into the lead after about a mile.The start is always harder than you want it to be. My heart rate monitor kept beeping that it was at or near my max, so I backed off a bit and settled into a good pace. The first half of the race I felt good, it seems I always have a "feeling crappy" part of my long races,this day was no different.After 4 hrs I took my bottle from the feedzone that had a soy protien mix in it. It has a slight vanilla taste and the taste was too sweet for me at that time. That and add the gels and jellies I had been taking every lap, my stomach was waging a war, although not quite winning(I held everything in thankfully).Took a water only bottle next lap and things settled down.Laps 10-12 felt like I was back to normal so I settled into a consistant pace and finished up in 1st overall, 6hrs-7min.,77.5 miles. In all, it was a good day:no mechanical issues, no muscle issues, although I need to figure out this whole stomach issue.All the marathon races I've done this year, about 4 hrs into the race I get an upset stomach.Any thoughts?