I just got a 1984 280sel euro w129. At 72mph my rpm is at 3500-3600. I guess I only have a 4 speed transmission with my m110 engine. Can anyone confirm this. I get 17-18 mile per gallon average. My manual says there was 4 speed and 5 speed models but I don't think its the original manual. My car starts in 1st gear from a stop.