1st of all: See if your fans are dusty, clean them properly and see if it helps.
2nd: Repair your cRPG. Start the launcher and tick the "Repair" box.
If that still does not help:
Download CPU-Z, start the game and the program, then see if it shows something suspicious. Such as your CPU or GPU getting extremely hot or overclocking.
Also, are other mods of Warband running smoothly?
Are other games working properly?