The M102 2.0lt carb had a 3.69 diff, same as the M115 2.0lt, M115 2.3lt, M123 2.5lt I6, and 240D
The M102 2.3lt fuel injection engine sometimes had a 3.69, sometimes a 3.58 diff. The 280E sometimes had a 3.58, sometimes a 3.46 diff.
Here in South Africa we typically had the 2.3lt M102 with a 3.69 diff and 4-spd manual, or 3.58 diff and automatic, to compensate for the high and dry climate.
The M102 was a major improvement over the M115 in terms of efficiency and fuel economy, but was never going to have a massive performance increase. MB intended for the six-cylinders to be the more sporty variants. The performance you mention seems to be typical and correct.
hmm, i looked at a 200gasser carb with automatic, and it had a 3.58, and im atleast 80% certain that was the same ratio i had on the 200T s123 fivespeed i have. (before it got the 2.47LSD it has now) might be a regional difference, in sweden the 240TD came only with 15" steel, and not 14" for example.
anyhow, the difference between a 3.58 and a 3.69 is not much, so little that i would not consider a swap "worth it"
@TS, i would look at the engine, as good as you can, that it performs as it should, are your exhaust in good condition, no catalysator that is clogged? is the timing correct, fuelpressure, have you had the exhaust "tested" that Lambda/HC etc values are correct?
the 2.3 is a rev-happy engine, down low torque isnt that much due to ratio bore/stroke, but at 3500rpm somewhere it should be happier,