airtronics rock crusher they have 2 versions. They have one slower one with tons of torque for a MT and one faster one with a little less torque for buggies and other samller vehicles.
You will notice from the specs that neither are exactly slow or weak powered.
More powerful slower -
http://www3.towerhobbies.com/cgi-bin...?&I=LXLSX0&P=7
Faster less powerfull -
http://www3.towerhobbies.com/cgi-bin...?&I=LXLSX1&P=7