The 87 300d with 5spd and the stock 2.64 diff climbs the Grapevine in 4th at anything above 60mph. I usually keep it around 70 climbing in 4th while passing most cars. 5th gear is purely for highway cruising on flat ground. 2300rpm at 75mph is a beautiful thing.

If you put a manual transmission in that W116 (even a 4spd) I bet you wouldn't mind the 2.47 at all. There's a huge difference in mechanical drag between the manual and automatic.

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CENSORED due to not family friendly words