www.ipttrans.com
or
www.levelten.com
Both can beef up your transmission. You might not like the price, though, for doing the whole unit. Alto also makes a rebuild kit if you feel brave enough.
www.altousa.com
I'm just doing the valve body and getting the torque converter changed to something a bit more loose for increased stall and it's about $1000. I think sending them the entire tranny is like $3200 or more for the complete "bullet-proofing". I'm not putting out enough power yet to justify that.