Why would my 93 f350 tranny went out from backing up a hill with my fifthwheel

Hard to say without a hands-on inspection. Check the linkage if it feels like its going into reverse when in drive. Outside of that you will need to bring it in. Use this link to find a good shop near you. https://repairpal.com/repair-shops Alex

Hello, additionally to Alex's good perspective, I would suggest that the vehicle is 25 years old, and to us in this forum has unknown history. And - is this a Power Stroke Diesel or a 7.5L V8? Is the transmission a C6 or E4OD? The E4OD automatic transmission in these vehicles is not known for exceptional longevity or the ability to navigate a load all that well, compared to current day transmission options. Additionally, pushing a fifth wheel trailer up a hill in reverse would be very stressful for your transmission, even a new one today. And although under proper load conditions the vehicle should handle it with no problems, it would be a stress nonetheless.

‘Stuff’ happens!