Do you mean too low? There 6:1 is what most production karts run in gearing terms, Yerf-Dog and Manco have a few karts that use a 10t on the jack-shaft and a 60t on the drive (axle), this does not of course take into account for tires but you might want to consider a 8t on the assembly for serious torque.
I do want to warn you however that a torque converter wasn't designed for going up hills or pulling out of ditches, it can burn up belts. If you want true torque without fear of burning belts and you have large tires the answer will be a large engine and a jack-shaft pure chain drive.
The mud slinging beast that was built at the shop a decade ago was just a West Bend 820 with expansion chamber utilizing a jack-shaft. It threw mud everywhere and climbed large hills.
Its just a suggestion, play with the speed calculator and see what works for you top speed wise.
By the way... is your avatar the Captain from the new Star Trek movie?