MBM seems to be more accurate than Asus Probe but is more difficult to set up. Either one will be fine to find out if your problem is heat.
If overheating does turn out to be the problem the quick and easy solution is to leave the cover off your computer.
Reseating the CPU may help if the thermal paste has dried out or lost contact ... no real need for high-end Arctic Silver type stuff, the thermal paste from Radio Shack works fine ... just be sure to do a good job of removing the old stuff.
A better
heatsink is the final solution.