I lost reverse?

Scan for codes as a first step, and you did use Mercon V? Filter change is not required during flush and fill.

I have a friend bring a scan tool over this afternoon. What we actually did was drop the fluid and changed the filter then added 4 qts of Mercon III by mistake? We then started it and found out that reverse was not right so shut it off and went and got 14 qts of Mercon V and did a fluid exchange. So after the filter change is was run for 2-3 mins with 4 quarts of Mercon III added to the 9 quarts of original fluid that had 44K on it. Ford people said that wouldnt have anything to do with it imediately slipping and said "just change out ALL the fluid and you will be fine" I did that and it didnt change anything. Reverse is now no existent and just before we pulled it in the truck would pull a mountain in REV?

Merlin 2021 thanks for responding so fast. I really appreaciate it as have no idea how much trouble we could be in here after a simple filter change?

Shift solenoids are on the valve body as is the filter, I would pull the pan, remove the filter and inspect for any pinched wires, also drain out the converter by removing the drain plug on it(if it has one), some don't! Put the truck back together, and put it on a flushing machine, the machine actually cleans the tranny, that's why it's used today! And the Ford manual does say transmission failure can result by using the wrong fluid, but I think after doing as I suggested and reading the codes, you will bo OK.
Post the codes here.