Agree with your sentiment about leaving things alone if they are okay.
However the 4L65E on the GTO's is just inside on it's factory torque limit (380lb-ft).
The 215hp V6 Lumina's here (4-door version of above) in the ME run 4L60E's and they don't give too much problem really so it isn't ALL down to heat as they are subject to the same running temps as the LS1 cars.
Yet the LS1 cars start falling over at 20,000kms [12,500m]and most have failed by 65,000kms [41,000m]. This is the 4L60E I know, ...and having talked to the GM Repair Facility Manager the overriding #1 problem is the heat and lack of an additional external cooler.
When they up-rated the engines (PCM) for the GTO to the same spec as the ME engines it coincided with GM fitting the 4L65E from the Vette into all MY2004 production cars of this type in all markets. This box has stronger internals and is re-rated 20lb-ft higher than the 4L60's 360lb-ft rating so time will no doubt tell.
A good pointer is to go onto LS1.com.au Forum and do a "search" on auto txmsn problems and fitting oil coolers.
The boys from "down-under" have found and sorted most of the problems, along with what works and generally what doesn't, and know how to avoid it with this car. Be a shame not to take advantage of the free, hard-won experience.
--- Sid447 ---