That's all true but that doesn't change the fact that the OP is loading down the regulator with displays that should be powered from a separate supply , not to mention he could avoid this problem by using a digital temp sensor. As long as he is running his display from the arduino 5V, whether it's powered from USB or from the barrel jack, the load is going to lower the Vcc and it will not be 5V and his temp reading will go up as explained in previous post.