How Can I Determine How Much Transmission Fluid To Add to My Truck When The Dipstick doesn't seem to be correct

I recently bought a 2001 F-150. The first time I checked the transmission fluid level, it looked like it was overfilled but the filler tube mount had rusted off and I figured it wasn’t accurate.

Last week I bought a new transmission filler tube from a dealer and installed it. When I took off the old filler tube, lots of transmission fluid spilled. I held the old tube against the new tube and they seemed to be the same size and length. I added a quart of transmission fluid and the dipstick seemed to indicate that it was filled. The transmission would still slip when I went up hills so I added another 1/2 pint (once or twice) until it stopped slipping. The dipstick is now in the DO NOT ADD range, but it was also in that range when there wasn’t enough fluid in there to function correctly so I just don’t trust it. I’m still worried that although there seems to be enough that the transmission is working, that there isn’t enough in it yet. I don’t want to overfill it either…

The way I check the fluid level is as described in the owners manual.

1. Warm the transmission fluid by driving 10-20 minutes
2. Park on a level surface (my garage)
3. Set the parking brake
4. Shift through each gear, pausing long enough to allow the gear to engage.
5. Clean off the dip stick.
6. Reinsert the dipstick fully
7. Remove the dipstick and read the level

I have the Ford service manual for this vehicle. According to the Ford workshop manual and my certification label, the transmission is a AODE 4R70W (tr code U). This model is also sometimes outfitted with 4R100.

Here’s my dipstick (not representative of the level, just illustrative):

The Dipstick part number is XL3P-7A020-CA

Youtube videos referencing the 4R70W seem to have a similar dipstick but one thing that worried me is that the dipstick looks more like the illustration in the workshop manual in the 4R100 section than the one in the 4R70W section. The illustrations aren’t great, but I’m just trying to figure out why the dipstick would read full and I’d still have slipping when I go up hills.

manual image for 4r70w dipstick:

manual image for 4R100 dipstick:

I’ve thought about dropping the pan and draining the Torque converter but even the specifications say to use the level indicator to refill it.

What should I do? Should I add an extra 1/2 pint to be safe? Do you think I have the correct dip stick? I could take a picture of the dipstick sticking out of the old filler tube to show how it indicates levels with respect to the filler tube hole on the transmission if that will help.