New guy here. After much patience and monitoring classifieds, I finally [towed home] a 1980 300cd N/A this past weekend, for a deal.

I’ve been working through some of the issues and have got it running pretty well. Fixed numerous vacuum leaks (or isolated faulty networks), replaced both fuel filters, adjusted valves, cleaned and freed all calipers, etc. Anyway, Here are issues that I am having a little more difficulty dialing in:

-shift points are uncomfortably high. Relevant data points include; 15hg @ modulator. No Bowden cable equipped. Fresh fluid. Overall vacuum reading @main manifold tube is 22hg steady.

-low power @ high speeds. Almost like it reaches some sort of internal limit at 45 mph. Even at WOT it cannot accelerate beyond 45. New filters have remained clean after test drives. Relevant data points; New clean filters. ADA dialed out. Linkage adjusted and sound. My next suspects are rack limiter adjustment, and tank screen.

I’m also suspecting the white vacuum valve bolted to the top of the valve cover. There seem to be two positions, and they seem to be dependent on throttle position. Not sure what this is called. Can someone Identify this mysterious component for me so I can study it?

Well it’s the end of the day, and my mind is dulled. Any insight to be offered to a fledgling enthusiast?