You may have been suffering the effects of hyponatrenia (low blood sodium level). During extended efforts in the heat, you can lose 1300 mg of sodium per hour, or more. Unfortunately, Cytomax has very little sodium - 100 mg per 16 oz, or 175 mg in a 28 oz water bottle. For a long hot ride, that's way too little sodium. You may need to switch to a different product, or find some way to take on supplemental sodium during the ride (salt tablets, pretzels, etc.).
Also, if this was one of your first rides this season in the heat, it may be an acclimation issue. The more you ride in the heat, the better your body gets at conserving sodium and other minerals. But, those first few hot rides each year can result in a very noticeable amount of salt buildup on your helmet straps, jersey, and skin.
Glad you survived it...cramps and chills when it's 98 degrees are pretty significant warning signs!
FWIW, I've been experimenting this season with a homemade sports drink, with the specific goal of avoiding cramps and electrolyte problems on hot, hilly, long rides (I'm training for the Death Ride). So far, it seems to be working - I've had no cramping issues yet this year (though that could be due to better training and/or good luck). If you're interested, PM me and I'll send you the formula.
Here are a couple of links addressing the issue of cramping:
http://www.ultracycling.com/nutrition/electrolytes.html
http://www.myodynamics.com/articles/cramps.html