Transmission Issues

[TheArctic]

Over the last three days, my 2001 740i’s transmission has been acting up really bad. On the first day, there was insanely hard shifting and a lot of clunking. It felt like the transmission was about to fall out of the car. But it was weird, because after about 10 mins it reverted back to normal. On the second day, there was no clunking but the car would shift at around 4500 rpms instead of the regular 2500 or so. Again, it would do it for around 5-10 mins and then go back to normal again. And today it was about the same as yesterday but 5 mins after it switched back to normal, it went back to high revving rpms and then stopped again 5 mins later. It could’ve just been a Mandela effect but I think I also felt a drop in power as well. No fault codes or lights are popping up. The car has ~243,000 miles and the transmission was fixed up around two years (10,000 miles) ago. Finally, when I tried to put it into manual mode to get it out of high rpms, it wouldn’t allow me to shift. I know the shift was working because I saw the number go from 2nd to 3rd gear, but it just instantly went back to 2. Anyone have any idea on what it could be? Any help is appreciated!
Update (I wrote this yesterday): Today I experienced more harsh shifting but not nearly as bad nor as long as the first day. The car seemed to shift higher than usual but not at the previously mentioned 4500 rpms. I was also told that the car has a Dinan tune on it but I don’t have the dinan cold air intake installed. Could that be something? It’s been in the car for a while though.

[CPHES]

Check the battery. My 540iT did a lot of that. New battery solved much of it. A Dinan tune should come with a Dinan CARB exemption sticker. Back in 2012, when Steve still owned the company, you could get the mods applied to your car with the VIN. Don’t know if that still works.

[TheArctic]

Update: The transmission seems to have fixed itself but a vacuum leak seems to have popped up. I don't think they're related issues though

EDIT: Also to answer CPHES's suggestion, I got the battery less than a year ago but still tested it regardless of that fact and it was fine