My stock 4L60E went 120,000 miles with no troubles at all. Religiously changed the transmission fluid every 50,000 miles. Abused the snot out of it every single time I could. I wanted, no, I needed an excuse to get performance mods done to it. Even held up to a year of abuse by the Radix. Finally, I just had the transmission done the way I wanted it for the last few years, so I can go drag racing this summer.