Great job on starting that taper, a big change in the mindset to get ready for the big day. Those cramps are odd if they are new, but dehydration and sodium deficiency from perspiration can definitely do it. You may want to make sure you're loaded up on calcium and magnesium as well before the race. But it does sound like dehydration as it happened at higher temps, do you drink fluids with electrolytes during the race?