There are no tranny problems. It is a gear ratio problem. Standard 1/8 center diff. Rock solid lst2 front and rear diffs.
I actually switched to an 8ight 48t spur gear, used a 12t clutch bell and used truggy tires on 17mm wheels. Brings gearing to a manageable ratio.
Use dynamite max life clutch shoes and you will be all set.
The only other thing you need would be a good steering servo with lots of torque. Double servo setup is junk.