WRONG FLUID IN TRANNY!! NOW WHAT?!
 

OK so I thought today was going to be a simple fluid drain and fill and replace trans filter. NOPE. I accidentally put in 3 qts of mercon 3 instead of mercon 5!!! AM I F*CKED?! I of course plan on redoing the whole thing tomorrow, however I did drive the truck and it acted funny so went straight back home, checked the fluid, and realized it was wrong fluid! so now it's mixed with everything else. my life is ruined! I love my truck (99 with 225,000 miles!) and I don't want it to die :( will I be ok after redoing it tomorrow? thanks for any advice u have.

dextronIII/mercon??

Never heard of mercon 3

But in any case you will be fine, I would drain the III and put in the V(5), the little bit that's left won't hurt anything.

What year and trans is it?

Any trans fluid that is Ford mercon and GM dextron III would probably be fine, Mercon(dextron III as well) was discontinued and Ford recommended/used Mercon V(5) and it is backward compatible to older Ford transmission

With the mileage and acting funny did you check to see if it was burnt before changing?