In a 1982 245 with B21F engine and M46 manual transmission, I get about 26-28mpg in 70% highway driving; the EPA rating, adjusted for the current reporting method (subtract 10% from city and 22% from highway to convert raw data to current window sticker numbers) is about 23 city, 28 highway.

However, in three other cars (with manual transmissions) that I have driven enough in the same type of driving, I've beaten the EPA highway mileage most of the time (in two of them, I've beaten the EPA highway mileage by around 10%). Have other people noticed the same thing (i.e. fuel economy relative to the EPA estimates is worse in a 240 than in other cars)?