Did that myself one time. Wait, it was the tranny shop that screwed it up and I fixed it. Had a full rebuild, ran fine for a few thousand miles, 1 and 2 were fine, 3rd started to feel like it was slipping. Eventually 3rd felt entirely like neutral. Ripped it down, found wasted front clutches and steels. Kept looking and found the inner hub of the front drum gouged from a burr on the input shaft. It caused a leak between the valve body and the clutches that eventually got big enough that they didn't engage.

Don't hold me to how technically correct that is - it's been a lot of years since I've been inside a torque flight.