well i have to say too many 2 count is a smart man actually changing the trans fluid BEFORE they burn up their tranny. I assume the fluid will remain in the transmission for 100k miles all the way up to the life of the transmission with the exception of what leaks and is replaced by topping off.

I had one customer a week tops to have the fluid flushed or simply a filter change even who was not an existing customer who had bought that transmission from us.
as in... until they burned the thing up they forgot all about it or were just uneducated in the basic maintenance needs of automatics.

Yes changing the fluid on a regular schedule increases trans life greatly and SHOULD be done anyways.

I am a fan of the full synthetics because they withstand higher temperatures and are rated to be good for 100k miles. I've noticed better shifts as well from the improved friction modifiers.

if you are just running dextron III then LUBEGUARD is a great product. it is an additive. the black bottle is the one to run in GM's I believe but its been a few years sense I've used any fluids that i'd want to add it to.