OK OK... Soooo you're saying you bought the truck this way without the transmission working. Here's the deal. The transmission was probably bad already. The previous owner did a trans fluid and filter change thinking that would save the transmission just like everyone else thinks. Therefore the transfluid didn't look all that bad. You're saying he put the filter gasket on wrong. That most likely blocked the intake from the pump or at least partially blocked. I really don't see how someone does that, but nonetheless it was done. You later pull the pan and find a black film on the bottom of the pan. The new fluid pretty much just rinsed out bad worn and/or burnt clutch material out of the drums and tunnel and it settled in the pan as the fluid was circulated.
Now that I know this, I'm going to go out on a limb, and not real far either, but going out on a limb and say the trans has some burnt clutch packs in it. And really can't say since the previous owner changed the fluid, there's no telling what was in the bottom of the pan when he changed it. It could have been a fist full of metal shavings or chewed up parts, so I won't go out on a limb and say it just needs a basic rebuild kit and be good as gold. It might be very well have some broken hard parts in it, like a broken intermediate roller clutch or sprag gear.
I'll suggest options in another post after you digest reading the bad news above. Hate to be the one, but yeah, that's my best guess on what has happened here. It now all makes sense too. The black film you talked about was telling me the trans was bad as soon I read that. But I was thinking this was a previously working transmission, and you simply changed the fluid and it didn't work. So this is a recently purchased truck, bought with the transmission not working.
