We have had no problems with drill motors overheating. They are in a dual motor gear box with the CIM motors and to my knowledge we have never tripped a breaker or heated up our motors. If you would like to see our transmission design it is already up on our website.......you may have to sort through some files to find it but I promise it is there.
http://neverland.ncssm.edu/robotics
Just go to the media page and then download the autodesk files. If you are heating them up in the short 2 minute period of competition then there could definately be a problem. Especially if you are getting them hot enough to desolder the motor leads and such. Also be careful running the boschs at really slow speeds for long periods of time as the fan is designed for a high speed motor and is not effective at low speeds.
-Aaron