Here a re few links to look at.
http://www.rcuniverse.com/forum/m_9248663/tm.htma simple mod to change gearing on your truck.
also this
http://www.comeseethis.com/gearing/gearing.htm your internal gear ratio is 3.19
Now, The truck comes with either a 17 or 18 tooth metric 48pitch pinion and a 64t spur that cant be changed unless you do the tb-03 mod. After the mod you can change everything to standard 48p gearing.
Hope this helps.
Mike