Reverse works fine, drive barely moves!
 

Hello everyone. I've been having an issue for quite some time now.
I got a 1990 4runner for free because the tranny supposedly didn't work. Basically, it didn't move whatsoever in any gear. I couldn't even feel it engage when I shifted into any gear (it is an automatic.)
Bought a used tranny, and BOOM it now engages in drive and reverse. Only problem is that it BARELY inches forward in drive. It goes in reverse seemingly perfectly.
There are no funny noises coming from anywhere as far as I can tell. Everything is hooked up to the tranny. I drained and refilled the fluid and it seems fine. I haven't refilled the diff oil yet and it seems a bit too thin.
One thing I should mention, there is one (vaccuum?) hose leaking air. I don't know how much that can affect it.
I apologize in advance for not having too much knowledge about diagnosing problems. I'm kinda stuck here.

The vehicle moves fine when in neutral??

Not that the calipers are seized or the Emergency Brake which might be causing your issue

Get the trans from a junk yard? Just pull it out and go get another if it's warranteed. Plug the vaccum line and see if it makes a difference.
Maybe the first gear clutches are smoked?

Are you sure that the fluid level is correct and are you checking it after it has hit operating temp?

I was starting to think that too, but is that even possible? Would they just unlock in reverse?

I got it from a small shop with 90 day warranty that sells used parts. I completely forgot about putting some fluid in the torque converter so I'm gonna do that this weekend HOPING that it's the only problem.