Yeah. I hate to say it but most mechanics are scammers. They might do good enough work but will never miss a chance to sell you extra stuff that you don't really need.
Auto transmissions are a challenge to be sure, but there are a lot of things that you can change in the vehicle. You might want to check your vacuum lines and maybe amount of vacuum at the transmission. Soft goods fail in the sitting around process and vacuum lines are soft goods.
I've bought several motorcycles (and a few cars) that have been left sitting for a long time. All of them have been at least moderately problematic. The sellers always seem to point that out as if it's a good thing. Even bearings will develop a flat spot if they sit in one place long enough and seals are really likely to leak.
Good luck with the repair. Oh, and one more thing. That physical thing will get worse-I just happen to know :)
I decided to get my ODB scanner out and check for pending codes, I knew there wasn't any hard codes since the check engine light wasn't on, turns out there is a code pending for P2111 , when I looked it up it is a throttle body code. I am going to get some CRC Throttle Body Cleaner and see if that cleans up the condition.
Makes sense that sitting for such periods of time some of that carbon that is usually built up may have hardened on causing it not to close all the way.
My initial thought was transmission since the old Dodge van would go to limp mode and it was transmission related. I hate that vehicles are so computerized nowadays. Give me a Holley 4 barrel and 4 speed and I'm good.
I let you know how it turns out. But thanks for those reminders about the vacuum hoses, those do rot over time.
Sult