Radiator leaking trans fluid

[HummerJim]

This is a pretty common problem on the H2. The same thing happened to me and I replaced the radiator and had an AAMCO rebuilt transmission put in, because water in the transmission fluid will chew up the transmission fast.
As for aftermarket transmission coolers I used the 1 ton Chevy cooler available over the Chevy parts counter. If you search, there are several threads on this with pictures. The only issue with the cooler is that in cold temperatures the tranny temp gauge hugs the 100 mark and it can be a little sluggish on shifting, however hauling a small 1000 pound trailer in the Rockies last August it stayed under 200 the entire time!