The salt all over usually means you were not acclimated. It takes 1-2 weeks of regular exercise in the heat to acclimate but as a medical professional, I guess you know that. Your plasma volume will increase a lot. You will sweat much more but will retain you electrolytes better. If you are fat, lose it.....this helps me. Wear white arm coolers and splash water on them. Evaporation is the best way to cool down. When you are descending, instead of braking, pull the bottom of your jersey open and let the wind flow over your entire upper body exiting your neck area, I find this very effective after a long climb.
The best advice I can give in extreme heat, slow down the pace. Recovery from overheating can take a long, long time.