Need options for new engine and transmission

I have the car listed above and a 2002 Oldsmobile Bravada. Both are rare and so dear to my heart. The Benz engine and Transmission is garbage! And I have a good feeling I may need a new dash for my truck. But if so? I need to get this running. But I do not want this thing to actually run like a Benz. It has to be a good displacement that can put a really good amount of power. That does good with fuel economy. As far a the transmission goes? It has to be either a four or a five speed automatic. I mean I would love a manual but my mom will forget about a clutch. I need options for my Benz because I am running out of options for my truck.