What rpms on the high does it need to run at to best better than my 24.5 in the city.?
need to keep it under 3000 rpms right? I run 44 psi tire pressure too.
Would a 2.47 rear end get better or worst? Options please need 30 plus MPG. 83 300D with auto with 3.07's

Like as said above, possible? Yes. Advisable? No.

The best I ever got was 574.2 miles in a tank. I had an unusually high mpg of 31.2 on that tank (and yes, I checked the tire pressure, I have stock wheels, how much I filled up--at the brim--, and my odometer is completely accurate). As you can imagine those last twenty miles to the nearest gas station having diesel were quite scary!

EDIT: didn't realize how old this thread was

Old but still going. I want to strip car of all unnecessary weight ad 2.47 rear end.and use GPS to get MPG. Not sure how much weight a can take out. But the alum hub caps.rims are lighter then. The 14 org. Alloys.

well i would just like to add something to look at for MPG is your tires what size are they?the skinnier the better...
I know with my own experience in my 85 300d that i could get 30-31 routinely if i stayed under 4lbs of boost and did only high way driving at no more than 4psi of boost (ie 45mph-55mph depending on grade) i live in southern mn with an alt of 1000ft and not much for hills or wind block.. also you need to coast to all your turns and stops only using the breaks to actually stop (if you NEED to)... its a process but doable
OR
you could take the easy route and add an auxiliary fuel tank in the trunk. I have a 16 gallon tank i put in my car for the long trips it increases my range to just about 1000 miles, only getting 25mpg or 1200 getting 30mpg...