Replaced 2000 Camry's A140E transmission

I replaced my 2000 Camry LE's automatic transmission with another A140E from the junkyard. My car has a 4 cylinder 2.2 liter engine with 190,000 miles on it. At first, the "new" transmission wouldn't begin to engage till the engine was revved up to about 1600 RPM and was completely engaged by 2200 RPM at most. So I figured, maybe some dirt had gotten into the fluid passages and was occluding a valve or something. (The transmission I got from the junk yard had one of its valve bodies scavenged, and dirt had filled that cavity till I cleaned it out easily with a vacuum cleaner.) So, after having driven it only about 20 miles, I replaced the transmission filter and the fluid, which, to my surprise, had already turned brown, and had just a shimmer of tiny metallic speckle, which I took to be aluminum since it was so shiny and didn't accumulate on the magnets.

The new filter didn't seem to help, but after driving a couple more days and a grand total of 80-100 miles with the "new" transmission, the car began to run perfectly -- and I mean as good as gold. And it continued like that for a week, which encompassed 350 miles of operating properly. But now it has become cantankerous again, though not quite in the same way as before. Now, it always starts out fine, but basically every time I come to a stop light, I don't know whether it will engage again right away when the light turns green, or whether it will take a while to get it going. But it's no longer a question of revving the engine to get it to take hold. It's more like either it works just right, or it won't engage at all, and you try it for a while and within a minute it usually gets going again. I should mention that I've been checking the transmission fluid level, and that's been okay.

Once it's engaged, it will operate properly indefinitely. My drive to work includes 20 miles of highway, and it never falters during that whole time, or any other times once it's engaged. There's no fluctuation in power or abnormal engine RPMs. Not till I come to a stop, and more than half the time, it works fine then too. It seems that reverse is more likely to fail than forward gears, and to take much longer to get working again. Low gear, however is no different than drive or second gear, so it doesn't seem dependent on the gear ratio.

So what do you think I should try next? Should I inspect the fluid again, and the pan, and look for clues there? I'm satisfied that the shift cable adjustment is correct. As for the throttle cable adjustment, I have to say I have not tried to fiddle with that, and I don't even know what its function is. It would be great if that were the issue. What affect to the throttle valve have on the operation of the transmission? I've tried to learn that, but haven't gotten a good answer yet.

Well, I appreciate you taking the time to read this. I should mention a couple more facts in case they're helpful. The transmission I got from the junk yard had been removed from a '97 Camry with about 85,000 miles on it. I kept my original torque converter because I had no reason to believe it was faulty. The problem with my original transmission was presumably a "seized clutch", if I'm saying it right. That transmission was permanently wanting to go forward, even when I put it in reverse or neutral (or even park, if I remember correctly). I think it wore out prematurely because I used it to pull a popup camper all over the country.

Can you think of some things I can try in order to diagnose this problem? Maybe I could measure the line pressure during a time that the transmission is failing. I could probably get it to fail in my garage some time. What about some inexpensive fixes to try? What can cause this knd of behavior?