I drive the 1980 300D.

As pointed out the lever on the valve on your valve-cover needs to be intact.
You can buy the lever separately from Fastlane (or your dealer) without having to buy the whole valve.
If the valve leaks, replace it. It is well worth it.

I will get some pictures of my configuration and post them.
It looks like you got it all though.

You may be experiencing the unique nature of these particular cars -
if you use the accelerator gradually the tranny shifts quickly, sort of bogging
the engine. I tend to drive more pedal to the floor and this causes the engine
to wind up to higher RPM's and cause later shifts. It is all in the driving technique.

At first I was overwhelmed by the 1980 vacuum arrangement and did not think I would ever figure it out.
Then (now) I realized how tremendously simple it is. You'll get it.

The 1980 has a simple transmission setup that works really well.
I have more trouble with the later turbo with bowden cable than I do this earlier model.

__________________
80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250