For 4 years I have consistently got about 38 mpg in my '91 300d 2.5 turbo when driving smoothly at about 60-65 on pretty-flat, mainly Interstate driving. I drive from Atlanta to Rome, Georgia and back a few times a week against the rush-hour traffic, and I only notice significant mpg decrease when dodging maniac cowboys driving 18-wheelers in convoys at 75+ mph as I approach Atlanta...
-sg