Sounds to me like your fuel mileage is good, but my 87 300SDL, which is a much bigger car is averaging 26.2 miles per gallon with most of the miles on the highway at 80 mph. My dad has an 86 300SDL and he never exceeds 65 mph and gets 27 to 28 mpg.

So, I would not be surprised to find someone out there with better mileage than you.

I use Amsoil fully synthetic oil. Use Redline most of the time - it will raise my mileage 2 mpg when I add half a container per tank. I calculated the costs and it IS worth it, but ran out and they raised their price, so have to bite the bullet and order some more soon.

Good luck.