For any NiMH pack (like the stock ones) will get a bit warm while running. If you can't keep your hand on them for more than a couple of seconds, then you have problems. A good practice is to let the packs cool before charging or running them.
NiMh will definitely get warm, especially if your running WTO! Did the same thing on my emaxx. Now I have since upgraded to lipos, no heat + lots of power!