Tranmission junk. yippee

Hey it's me again, with some goodish bad news.
So after seeing pennymans coolant temp switch OD hack like 3 times atp, I tried it out and it actually worked holy crap.

But this gawd awful whistling noise I hoped was just a vacuum leak stopped when the truck dropped into O/D, so transmissions probably cooked. feels a little icky and takes a second to drop into it too. hoping itll heal itself, its an auto after all. if not ill get the fluid and filter swapped. r4ac1 btw. just wondering if anyone has ever gotten the rebuild and if it wasn't super expensive. also curious if there's any shift kits for the r4ac1, ik it's a copy of an a500 but idk if their specific or not.
as always, thanks for the read