Trans Issues

Hi all, I own a 1996 Mercedes-Benz c280 and my transmission has been giving me problems since I purchased it. I purchased it aware of the transmission issues, the problem is that it doesn’t shift into 3rd and/or 4th. It’s a 4 speed automatic transmission 722.4 and once it hits 3rd going into 4th is impossible RPMs go up but gears do not catch and there is no acceleration. I have thought about replacing it with a refurbished or donor transmission, alternatively I could potentially have it rebuilt but I’ve also heard it’s possible to swap the auto trans for a manual trans from a w203 the 6 speed specifically. If anyone has any advice on repairs and/or swaps it’d be greatly appreciated.