Could any harm come from mixing ATF+4 with Dexron III? My 92 Dodge Spirit with the 3 speed auto had it's original transmission (at 304836 kms) just kinda get lazy and die over the past month. It wasn't shifting right at first, then it was hesitating between shifts. It evolved into slipping between shifts, then not shifting at all, then just dropping out of gear constantly. I had a couple of unlicensed but knowledgeable and honest mechanics replace the bad tranny with a JY unit that had 186000 kms on it. They had it done in less than a day, that included taking the replacement tranny out of the donor car, then taking the one out of mine and putting the replacement one back in. Total cost to me was 325 bucks, that included the tranny, labor and an ignition lock and key that also needed replacing. The replacement tranny works great, except I think they left the speed sensor unhooked because I now have no speedo, odometer, cruise control or TC lockup. Now my main question is this, I want to change the fluid and filter, what fluid should I use? The A413 can use either Dexron III or ATF+3/4. I don't know which fluid is in the tranny and I don't know if it's safe to mix the 2 types. I assume the tranny has Dexron in it. I'd like to use ATF+4 as I hear it makes for smoother shifts but I don't know if it's safe to mix the two fluids. Help?