WoW .. that sucks! Sorry to hear this happened to your Rig but atleast it sounds like you cought it in time! I installed the Tru-Cool external Tranny Cooler for this exact reason. Tooo many H2's were blowing the Transmission line and spitting Trany fluid into the Radiator and Water into the Transmission to the tune of a $4000.00 repair bill!!!
I paid $150.00 for the Tru-Cool MAX transmission cooler about 6 months ago and re routed the Transmission lines out of the Radiator. IMO it's the best $150.00 I spent on my Rig.
Here is a good thread to read regarding this problem:
http://www.elcovaforums.com/forums/showthread.php?t=23002&highlight=external+trans+co oler