Transmission issues and fluid type

Hello

I had a problem with my 1981 F150 (automatic) where it would not go into gear reverse or drive when it was cold, I had to move the gear stick back and forth to engage it and it could slip out until it warmed up. I checked the transmission fluid and it was low, so I checked the dipstick and saw it needed to be M2c138 cj oil for my C6 transmission (Has a K for the transmission on the door label).

I bought some FRAM multi-vehicle ATF that stated 'Meets DexronIII/Mercon performance requirements'.

I added one quart and ran the truck and noticed that it now takes higher revs and higher speeds to change gear, feels like it has to get to 30-35MPH and 3,000+ RPM to change to second gear and previously it felt like it changes at 10-15 mph. It's also a lot more clunky when it does change gear.

When I went back online it said the FRAM fluid was not compatible with my truck.

After the drive, I checked the dipstick and it still should low transmission levels, kinda of kicking myself for not checking it before.

What could the problem be?

Do I add more transmission fluid and what type should it be?

Thanks
Paul

This is a 1981 Ford 150, 302 V8, 4x4, shortbed.

I would drain and refill the transmission and the torque converter, for two reasons.  First, you obviously have an incompatibility in the fluids and need to start completely over.

Second, I think that your transmission fluid is "worn out".  ATF has several additives in it that do important things, and they wear out over time.  One of those important things is to cause the rubber in seals to swell, and when it wears out the seals leak and the shifting isn't right.  Another thing is the friction modifier that causes the clutches to lock up quickly.

I've seen this many, many times where a change of transmission fluid makes a slipping transmission work much better.  But at least half of the fluid is in the converter so you have to change all of it.  And you want a good quality Dexron-II fluid.

Where can I get Dexron II, most places have Dexron III only.

I meant to say you should go with Dexron III.  That's because everything I've read says III replaced II.