By suffer do you mean they look a little wilted?
In really hot conditions, wilting is the plants way of preserving water. Now, blow cold air on me if I'm pontificating on something you already know and I'll scurry back to my warm rock.
Water is drawn up through the plant from the roots by the process of transpiration, an evaporative process that takes place in the leaves and stems. Water evaporates from the stomata, pore-like openings found usually on the underside of the leaf; and CO2 diffuses in to be used in photosynthesis. The guard cells that control how wide each stoma opens are in turn controlled by the amount of water in them. They swell when full of water and all the stomata open wide. When water is evaporating from the stomata faster then it can be drawn up from the roots, the cells in the leaf loose turgor, including the guard cells of the stomata. As the leaf wilts slightly, the stomata close and the plant stops loosing water as rapidly. As the heat of the day passes, the rate of evaporation does not exceed the rate of transpiration, and the plant perks back up.
So, as long as the soil around the roots is good and moist, there's nothing wrong with your peppers being a little droopy in the heat of the day. Personally, I consider that the kind of stress you want on a pepper to ramp up the heat a bit.
Whew! Ok, I need caffeine now.
