Transmission help...
 

Ok, sister-in-law has a 96 Sable. It started doing the hard shift into first from a stop.

I hooked up a Snap-On scan tool, and watched the shift solenoids as it wasn't a constant thing at first, but became more common and hit the point where when you were driving it would "drop out of gear" and into neutral, and then back into gear.

So when in park, the solenoids read:
A: OFF
B: ON
C: OFF

When in drive (or 1st), when the car *would* go the solenoids read:
A: ON
B: ON
C: OFF

As you drove slowly around the yard, the car would drop back into neutral and the reader showed the solenoids were in the first list.. when it started moving again it showed the solenoids were now in the second list.. and it would keep doing this for a minute or two before it just got "stuck" in neutral and wouldn't move (and the solenoids were back to the first list.. same as in Park)

I tried switching solenoid A with solenoid C to see if that made a difference.. and it didn't. Also, there's no Reverse anymore (this was the case even before I changed solenoid A and C)

The kicker to me is, if you unplug the main harness to the transmission (located right next to the side pan cover.. white plug, flat on one side, and curved the rest.. wires from this plug lead internally to the solenoids and TCS), you get drive back (I forget, but don't think reverse is there even with the harness unplugged).

This sound like a sensor, solenoid, or broken wire to me.. but I don't have a factory service manual to find any diagnostic steps and/or suggestions as to what may be wrong.

There are no codes, unless you unplug the harness which obviously spits out codes for solenoids A, B, C and also the Torque Converter Solenoid or whatever.

Has anyone experienced this before, and what did you do to rectify the situation? I don't want to replace the transmission as it's a car she no longer uses, I'd rather mess around with the thing and try to fix it "the hard way" lol.

Thanks for any info, input, help, links, whatever you can pass my way.