I have been on a strict zone diet prepping for a tourney. I posted in my log this morning that I am just exhausted. I have however already hit my target weight with 18 days to go. Before you start adding in CHO have you tried upping the fat intake. That is what I am going to tinker with over the next couple of days.
The biggest thing that I have done pre-grappling to change my performance is to start sipping a Gatorade (loaded with sugar and CHO I know, sometimes I drink a G2 depending on how I feel) at 4:00 PM on the days I train in the evenings. That has helped me enormously make it through 2 classes and grappling. It has been quite hot here in FL so I am totally with you on the sweat deal.
Immediately after training I stop at a 7/11 and grab a 16 OZ chocolate milk and a zone bar. I will eat and drink those along with a 32 oz water on the drive home. Once I am home I will eat an additional meal depending on the way I feel.
Hope this helps. I don't know what part of the country you are in but working out in the heat will sap all the energy out of you no matter what you ate or how often you have trained, especially if it has just recently gotten very hot.
What we think, or what we know, or what we believe, is in the end, of little consequence. The only thing of consequence is what we do. -John Ruskin