Re: Turbo400 stuck in drive ALL THE TIME
since it sat with low fluid for a long time, I'd try filling it like you did, running it around local roads until it got HOT. Maybe once it all circulates it will loosen up. I would try putting it in 1st, so to prevent (hopefully) it shifting when away from the house, and then bump it up at 5-10 as you pass your house incase it locks up when it shifts or something. After moving it around, check fluid again and top off, might take a couple times.
If it feels like reverse and forward are engaged, I'd try letting it idle a good while staying in the car to hold brakes incase something happens.
Is there any chance it had a transbrake or something?
1967 El Camino Malibu - Deepwater Blue
ZZ4 350, FiTech 600 complete!,Roadmaster tank, 700R4, Underdash A/C in progress, JGC Steering, 1990s truck serpentine.