My guess is the Dealer guys pulled the computer codes and it showed that the Torque Converter was beginning to slip.
I believe that the Dealer's shop did not install the seals correctly and should stand behind their work if in fact the oil is Tranny fluid. Easy to tell!
I too have a Ford f250 gasser 460 but has the e4od tranny, 1994, believe yours has the e5od.
I started having trouble with the Torque Converter and the computer put the transmission in limp mode... Shifting so hard it would nearly break your neck. Computer Codes said TC is slipping.
I took it to a reputable Transmission shop and had a discussion with them. They asked if I tow'ed anything.. Yes was my response, I have a 3500lb camper and pull a 2000lb VW baja. They said they could upgrade the TC to a diesel type and put a performance kit in the transmission to handle the extra load.. Ouch on the price... $4,000. I had them do it and that was 40,000 miles ago.
Hopefully you can get this resolved. That F250 is a great truck.
Jim