Just took my '91 on a nearly 5,000-mile trip from SoCal to North Dakota and back, mostly on back roads. Spectacular drive. And stunning MB performance.
I also set a new economy record: 36-plus mpg, with no A/C. Most tanks got between 33 and 35 mpg. Got 32 on one leg through SD -- driving between 80 and 90 mph. Worst economy: <30mpg from a tank of freak fuel in the ND Badlands. Or the 31 mpg across the Mojave with full A/C.
The car was also immensely comfortable, with no back problems. Car with one passenger and loaded to the gills (with squeezebox and Igloo in the back seat). Our final drive was 775 miles from Evanston, WY to Los Angeles, CA.
Plenty of passing power, even above 8,000 feet, thanks to the turbo feeding the car's rather small 2.5 liter powerplant.
I had two concerns, however. The first was a tendancy for my 300D to run up to 110C on long uphill grades with the A/C on and outside temps from 95 to 105F. I frequently had to shut off the A/C to control temps _ and my anxiety. Other than the grades, the car ran at a steady 85-90C.
I fear a new radiator may be in order.
The other downside was no power off the line at high altitude. In Manitou Springs, CO, it was floor-it-and-wait -- like watching a firecracker with a slow fuse. But when the turbo spooled up, the car ran like a rocket.
The 300D 2.5T is a highway warrior with fantastic economy for a car its size. I can't think of a comfier car with longer legs.
But it's a killing machine: I killed two birds and a badger on the highway.
And after leaving L.A./Las Vegas metro, I only saw to MBs the entire trip.