Under the dash

I had a similar issue with mine sticking in 3rd. It turned out to be the input/output speed sensor more recently. But I've also had issues previously with my neutral safety switch sensor. I can't remember which code I was getting, but P0750 sounds familiar. Check your sensor, it'd located directly under the battery plate on the top of the tranny. Mine went bad because if a faulty battery. Which leaked onto my sensor and corroded it... Twice. It's plastic and easy to see if it's damaged. If it's either the input or output sensors, they're easy fixes too. I'm a girl and think it far simpler than enduring another manicure. Lol, quicker too. Good luck, and hope it helps.