[oil pan 4]

I kept the intake manifold and upper plenum the same. I actually tried to change as little as possible in the change over.
Highway driving it stays in top gear with the converter locked. Not much change there.

Problem with turbo versus non turbo is the OEMs and their cookie cutter one size fits all turbodiesel applications.
The OEM is motivated to put on the smallest cheapest turbo that will get the vehicle sold off the lot. That's great for start stop city driving, bad for highway and towing.
The OEMs have a bad habit of poor execution of great ideas.
When GM started to turbo charge the 6.5L same thing. Fuel economy really didn't improve much. They used a small turbo and crappy intake and exhaust piping.
The only OE part I used for my turbo build was the N/A intake manifold that I altered slightly for use with big turbo piping. I determined that the nonEGR N/A intake manifold gave the best fuel economy after testing 2 of the OE turbo intake manifolds. Everything else was military surplus, aftermarket or stuff I made.

Lets pretend I do not know squat about the old VW diesel. Are we sure they didn't change anything else drive line or fuel injection pump wise?

The old VW diesel is the worse I have ever seen as far as turbo and fuel economy loss.