How much of a benefit is it to switch to synthetic transmission fluid?

[steppinthrax]

Transmission fluid you?re only supposed to change around 30K or at least that's the manufacture recommendations. Thinking Mobil 1 Synthetic Transmission fluid

 

[radioouman]

It will last longer before it breaks down.

Chrysler used ATF +3 during the 90s and then switched to ATF +4 in the 2000s which is fully synthetic. They recommended it as a replacement for ATF+3 in the older cars. I switched my old truck over to ATF+4, and the transmission fluid no longer breaks down after 10,000 miles or so. (I mean that the old fluid would make it shift really nicely for the first 10,000 miles, and then it would start shifting worse until I changed it again.) ATF +4 seems to preserve that shift quality longer.