I was fairly fit going into chemo and rads, and my second round of cisplatin had to be reduced by 25%. I was surprised too, but my MO said it happens. Sometimes they skip the third round of cisplatin, depending on your reaction to the radiation at the end of treatment. If they think the rads hit you way too hard they won't give you the third round of cisplatin.
Sounds like you are handling treatment super-well. Good for you!

Left tonsil SCC, HPV+. T2N0M0. Tonsillectomy 3-07, bilateral radiation, cisplatin 3x, Tx completed 6-06. Clear PET 4-01-2008.
Thyroidectomy 5-9-08, resulting in permanent surgically-induced hypoparathyroidism and adrenal problems. Bummer.