When to change trans fluid?

When should I change the trans fluid for the first time?

i did mine at 50k miles

If I remember correctly the recommended interval from Ford is 60k

I would only follow the Owners Manual if you drive "normally".
If you off road your truck regularly or tow regularly I would move that interval up.
I pulled my compact tractor and trailer up some pretty nasty mountains and through some tough 4x4 trails resulting in the tranny running hotter (not over heated) for an extended period of time so I changed it at 25k. I tend to go by types of miles rather than miles

Isn't there a breakup in the owners manual for scheduled maintenance? One sections for regular use then one for towing/hard use?

I did my motor and diffs at 1k miles, transmission at 10k miless. I do drive it hard, so I'll be doing them all again at 20k. All fluids swapped to Amsoil.