ATF +4 is a synthetic transmission fluid. as such, it is more thermally stable than ATF+3 or others. as mentioned, there is a TSB chrysler issued stating that it is safe to supersede from +3, the only models it mentioned not to do such was 99 and older minivans, as they would not be able to break in a new torque converter clutch if replacement was required. i use ATF+4 on all my vehicles, expensive, but worth it.