2002 forester transmission issues

[Caleb.s78]

I have a 02 forester, the engine runs fine, but on start up the oil at temp light turns on, check the fluid levels they are fine, did a fluid flush and a filter ( made sure to use the correct ctv fluid) car will go into gear but feels like it will only maybe go into second gear I think it that the fluid isn’t building pressure, what are any other reasons this might be happening
Also what years of transmission can I use if I go the route of just swapping trannys I’ve heard from my local wrecking year that only 2002 and I’ve heard from my local Subaru dealer that 1999-2002 will work I’m inclined to trust the dealer for obvious reasons

There are no weird noises or smells either