I tend to agree with a fuel supply issue as in starvation (pickup screen in tank?) or maybe air in the under hood fuel lines (some bad o-rings) In these cases engine would run reasonably well at low power but would surge, buck and struggle under power. If you can, park the car on an upgrade with the nose higher than the tail overnight. If it won’t start the next day, you’ve got leaking o-rings allowing air into the system, and gravity allowing all the fuel to drain back to the tank.

As for the strange shifting- when the trans on my 99 E300 started to go, it would either not shift out of first at high rpm or suddenly change gears out of 5th or 4th and drop down into first unexpectedly and at speeds way higher than it should have.

How many miles on the car? My trans started the strange shifting around 130k mi...

J.G.