When you have that problem --- runs slow, and seems hot, it's likely there is some software process that is the culprit.
You can check in your Activity Monitor. Make sure it is set to show All Processes, and not just Your Processes.
Look in the CPU tab first. You can sort the list by %CPU (Each time you click on the menu header in the %CPU block, the list will reverse. You want the highest numbers at the top

)
What are the top 5 processes, and the percentage numbers listed?
Best time to look at this is at the time that you have the problem...