2002 F-150
4R70W transmission
130,000 total miles
Originally flushed (changed to Amsoil ATF) at 1,500 miles. Second fluid change was at 71,000. Now at 130,000 miles on second flush (or 59,000 miles without a change).
Performance differences are not noticeable but the transmission shop (at a large Ford dealership in South Texas) that changed at 71,000 miles was amazed at the lack of degradation of the transmission fluid. The tech stated that most ATF fluids are fried at 30,000 due to the South Texas heat. He also said that the 4R70W is particularly known for failure without regular transmission fluid changes.
Perhaps the change intervals can be attributed to the large external transmission cooler installed at 1,000 miles; however, the tech at the Ford dealership said most of the large Ford trucks already have transmission coolers but the fluid is very dark at only 30,000 miles (the ATF fluid was not dark in my truck at the 71,000 mile change).