You've hit on the cause of your declining tomato yields. Although tomatoes are a warm-season crop, it can get too warm for them. Generally, tomatoes grow bigger, better, and faster the warmer the weather. However, when daytime highs regularly top 95 F, the plant's pollen can be killed. With no live pollen to pollinate the flower, fruits fail to develop. Varieties such as 'Heatwave II' tolerate the heat better than do others. If you're not growing a heat-tolerant variety, wait for the weather to cool down; normal fruit development should return. Other warm-season vegetables sensitive to excessive heat include pepper, eggplant, pumpkin, squash, and cucumber.