So awhile back in my 98 4x4 4.6 I hit a ditch and punctured a hole in my rad and overheated my transmission and it lost forward gears. So only had reverse.
so I bought a used transmission from a friend and just installed it.
I pour about 5L of fluid into transmission and turn truck on and hear a whining noise that sounds like when your low on power steering. So I assumed that's what it was.
I run it through the gears slowly and put back into park, shut truck off and put another maybe 8 or 9 L into transmission. Turn truck back on and look under it and notice this noise was coming from the torque converter. So I start running it through gears again and notice reverse tires start spinning. Drive second and first nothing happens.. so I'm not sure if that's because I still need to add more fluid or if this transmission is messed up too.
Not really sure what my next plan of attack should be...

One more note is that I did not flush the transmission lines before installed the new one I didnt think that was necessary

And tips or advice I'd really appreciate because all the rust on this damn truck it has been a pretty big job doing a tranny swap and I'm hoping hi dont have to change it again hahaha

One more note. I haven't actually fully warmed up the transmission because the noise kind of concerned me when I realized what it was

 

If the fluid was burned and black in the original trans some of that "stuff" got circulated through the trans , converter and cooler and should have been flushed.
Don't know for sure , but would suspect some of that got introduced to the replacement trans. Dirty fluid doesn't always cause a trans to make noise. Are you sure the converter was fully indexed into the pump gear in the trans when installing it?