i read your signature. it says the sdl has 300k miles. NEVER had a trans rebuilt? NEVER changed the atf before? supposed to be every 30k miles. you're on fumes now.

try this. drain the pan and keep the fluid. refill with with 1 new atf. then refill with the used atf. this way you gradually introduce fresh fluid. gonna take a couple of years if you do this once a month. more work but cheaper that a trans.

me, i'd pull the trans and get it done. 300k is a lot.