Leaking and slipping

This is about a Ford F350 Chassis RV.

We purchased this unit very early last year. We fixed it up and set out on the road. It was running fine until about August/September of last year. It seemed the transmission was slipping. My husband would put more fluid in and it would smooth out. Rinse and repeat.

We did not do anything about it then since we were going to be stationary for the winter. Not to mention we could not afford a mechanic either. However my questions are not about money or when we should have seen a mechanic. We stayed put until May of this year. The same thing was happening. It would slip and after adding more fluid, usually about a half quart, it would smooth out.

We were heading west to Rapid City to start visiting the west. We were hoping to get there and then get the tranny looked at.

We almost made it.

We had to add fluid more and more as it kept getting low. I do need to add that up until this point we didnt know where the leak was. There was never any drops or puddle under the vehicle. We surmised that it was happening while driving.

We got from Ohio to South Dakota before things really went bad. The ambient temperature was through the roof. Upper nineties. May not sound hot to some but was killer for us. We made it from Chamberlain, South Dakota to an RV park right outside the Badlands. About one hundred and thirty miles. We went through a gallon of transmission fluid.

The next day we made it to Wall (twenty one miles) and used another gallon. Needless to say we could now see a leak under the vehicle. It was near the passenger side front wheel, right around there. We got towed to a mechanic shop that said we needed a "new" transmission While we were hoping we did not need it we figured we might. So we made the appointment to get the transmission rebuilt.

Fast forward a couple weeks and they call and say that the transmission is fixed and works perfectly. Oh, but your catalytic converter is bad and needs to be replaced, to the tune of over a thousand dollars, because that is what caused the transmission to go bad to begin with. They will void our warranty if we do not get it fixed.

This leads me to my questions.

1. Can the catalytic converter cause that kind of damage?
2. Why did not they tell me about it to begin with? Should this be something that had been discovered when they checked the transmission?
3. What could have caused that kind of damage to the transmission?

Thank you for any help you can give!

Rachel