As far as I know, the non-vacuum controlled transmissions in the 123's are adjusted with the aforementioned rod system and there is no mechanical adjustment on the driver's side. I may be mistaken.
If that linkage is binding, lubricating it may solve your problem without any adjustments.
My 77 300d was pretty doggy too. It is designed to start in 2nd gear. It was a little more peppy if it started in 1st but nothing like a turbo model. I do live a mile high.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13