If it's a standard transmission and isn't getting into top gear, that problem lies entirely with the driver. If it's an automatic, you need to count the shifts to see if you are hitting fourth gear. Put it in L to make sure it starts in first, then back to D and count the shifts. It's not unheard of that these automatics fail to carry out all the necessary shifts.
MB diesels are not slow turning diesels like older truck diesels. They are high rpm diesels.

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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