Um, check your odometer.

EPA ratings for an 85 300TD turbo were 22-25 mph when it was new.

I've been keeping extensive records for 4 years on my federal 85 300 TD turbo and those are exactly the numbers I get (140,000-170,000 miles on the clock).

I once got 27 on all highway miles drive back from Maine (75 mph, 3 passengers plus luggage, windows up, AC off).

I would guess that unloaded and with a light foot, you might be able to get 30, but your numbers are way off for that car (unless you're selling it on E-bay).