Well it kinda stinks I didn't see your post before you did the fluid and filter changed, because I would have highly recomended with the filter down you replace the solenoid pack it is on the inside and you have to remove the filter to get it, it is common for it to go bad and cause some symptoms as you describe, also when you pull the pan make sure you reseal it with black RTV as was done with the factory trans filter kits come with gaskets and these pans were not designed for gaskets it causes leaks if you use the gasket. How bad was the old fluid dark red smelly looked to have any little material in it if so I don't need a scanner to tell you the clutch packs are probably going or gone. I never like throwing in parts for no reason, it is good to get it scanned but most places will just tell you to rebuild it, the 42 LE in these cars is actually pretty strong but if you run them out of fluid they die, regular ATF causes it to act real crazy wont hurt it unless you keep trying to drive it like that, you could pour in lubeguard using the mixing ratio, ATF+4 is regular ATF mixed with 4 additives, an antifoaming, friction modifiers that are necessary for the clutch packs to operate properly, I am sure there is more, this is what I remember being told in school. People are probably going to be mad I said that or tell me I am wrong thats ok cause I don't rebuild transmisssions or use Regular ATF customers hate paying more but hey I hate seeing cars comeback. You can test the solenoid pack if you want to be sure, its just too bad it is inside the pan on this transmission so that means you will loose all your new fluid and I know it is expensive. You will need to use a ohmmeter, and might want to see if you can find a diagram that tells you where to measure it from and what the value is supposed to be.
I would say that the trans is pretty much to that point, you are either going to try the solenoid pack or I would get a used trans from a yard and before you put it in pull the pan look at the magnet and look for a lot of shavings if it has it bring it back, if the fluid if dark or has little material in it bring it back get another one. Problem you will have is 1 getting the car up high enough to take it down, 2 you will snap a few bolts on the engine member getting it off, 3 trying to loosen the bell housing bolts sucks, especially since you have the heater tube running there and you don't want to snap that thing they are dealer only and expensive. 4 you wont believe how much really has to come off to remove the trans, 5 the bellhousing bolts have threadlocker on them so you need a nice big cheater pipe to break the bolts loose. Its not a fun job, theres worse out there, but it's not fun or super easy.
Goodluck....