Dave,
Here is a video of my son messing around on the go kart (see other post about specs) This was before the go kart had the spacing between the jack shaft and engine fixed so it had less power than it does now. With that said, you can still see it spinning out as it goes up hill. The only reason the kart didn't make it up the first time is because my son let off the gas :-)
If you go with the 40 series torque converter, you will not be disappointed.
https://www.youtube.com/watch?v=B18ybsN8Sf0