That is exactly what happened when my old trucks 700R4 went out, but at a lower speed.
Sounds like it's time for a rebuild/replacement in your future. Go easy on it until you get the money. Do youself a favor, and try to remove/install the transmission yourself. It will save you a ton of money.
You could do a few checks if you like. It "may" be something simple & replaceable, but I doubt it.
Do a search on this forum & the 5.0 Tech for things you can check. Hopefully a valve is stuck, or your front pump is bad and you caught it early. 5.0 tech will have much better info then here (more technical transmission rebuild info).
Scott