As my mechanic told me some time ago, you may as well run what you have until it breaks and then replace it, you won't get anything for it trying to sell it anyway.
I'm currently in a similar situation with a 5r55 in my 2010, I do track days, have approximately 20 track days on it and have overheated the trans several times now, just turned over 52,000 miles and she's still hanging in there. I've added a B&M racing trans cooler, JDM Catch can, and a Performance Automatic larger pan to try to resolve overheating but not much luck. I'm only pushing 390rwhp.... I've also upgraded radiator, heat exchanger, and front grille. Today it's getting MMD hood vents put in.... I've stuck a bunch of cash into this trans overheating problem with not much luck yet.... at this point too much to turn back or sell it.... I have no idea what I'll do when mine finally dies....
As said previously, other option is you may want to consider trading now....