First, I'll make my ask. I'll post more info below if anyone cares. I'm looking for a nutritionist that understands and has experience with long distance racing. Please reply if you know where I can find one.

Back story:
I've been doing long distance triathlon for around 8 years now. I've completed multiple full and half IM distances. This year, I experienced major dehydration at IMTX. Blacked out around mile 8 of the run and was pulled off course. The strange part for me was that I consumed as much liquid as usual and I live in TX and workout in the heat often. Since IMTX, I've begun experiencing dehydration even sooner in workouts (as early as the 3 or 4 hour mark). I have reasons to believe that my body is not absorbing liquid like it should. I've met with my doctor for kidney, electrolyte, potassium, etc tests. All came back good. The two times I've ended up in ER for it (once at race and once at home), they tested my blood and all levels were normal as well. My doctor is now recommending I consult a nutritionist. However, I want to make sure I find one that understands long distance training and racing.

Side note: My tongue turns white on long workouts in the heat. Not sure if it's an imbalance of something or sign of dehydration. Also, one doctor told me that when you reach your threshold (like I did at IMTX), your body can have a much lower threshold for quite some time. This seems that it may be true. However, I'm still not sure what caused it at IM as I believe I was racing well within my limits.

Thanks for any recommendations and please feel welcome to share opinions. I'd love to find someone else that has experienced this.