How are you repairing the connections, for my information?
A little backround info:
Transmission Oil Cooler (TOC) lines were a sore spot for GM for quite a while. I'm not sure if they've worked out the fix yet, since I'm no longer working for that industry. However, during the late '90'*, GM and their suppliers were feverishly working to resolve the problem you just experienced. TOC lines were failing, at the crimped connection, during extremely cold weather.
The source of the problem is the grooved cross-section of the pipe and how it works (or doesn't work sometimes) with the hose liner tube to seal the connection during crimp. There was much design and testing activity to verify and change the groove design, manufacturing methods, and test methods during that period. Not sure what the end result was, as I left before resolution of this problem (to move back to Florida).
Sorry for the windy blah, blah, blah, but thought you might be interested in the root cause of your problem.
Mike: 1997 SE w/ 183K, aka White Horse
, Gutted Airbox w/K&N, drilled 180* t-stat, tint all around, clear corners w/SilverStars, "PONTIAC" light up tail, PEMs, NGK TR55s