Our trip to pick up Highlander was an all-but-empty truck with a full Retrax bed cover and food for a couple of days. After our excursion to Keokuk, Iowa we filled up and calculated a net mileage of 15 mpg.
The next day we hitched up and after a short stop at Beilstein for adjustments, we hit Highway 61 and headed for home.
The Allison 6-speed transmission behind the GMC Duramax diesel has a trailer mode that eliminates the overdrive and changes shift points. We rolled up the entrance ramp and it felt like we were hauling a load of post holes. Smooth and effortless. The Duramax 6.6 L (403 c.i.) is rated at 397 horsepower and 765 ft/lbs of torque.
Even with some slightly rough patches on the road - this is Missouri, after all - the trailer pulled straight and smooth. Stopping was effortless - the trailer brakes were dialed in after we picked up the rig and were perfect. When our forward speed hit fifty-five, the transmission settled down and we ran at a fuel-friendly 1500 rpms.
I watched the fuel gauge as we drove west on a perfect August afternoon. It dropped steadily, and by the time we reached our double-secret undisclosed location where we were going to store the rig for a while, the needle had dropped just below a quarter tank. The tank is thirty-six gallons.
We cruised back to the house and I got up the next morning and filled up at the HyVee. 10 mpg! I know that doesn't sound like much in a world of hyper-miling and smug Prius owners, but 20,000 pounds of rolling stock ain't no Prius.
Some highways are better than others when it comes to places to rest and refuel. US 36 across Missouri isn't great, but there are options. We only saw one accessible fuel stop - accessible means you can drive a 50 foot rig into and through without getting caught in short turnarounds and dead ends. Worst case scenario is that you wind up backing out after refueling. It's possible, but backwards is not my favorite direction - it requires two people, Forward only takes one.
We will spend more time in the future researching routes and available fuel before heading out next time.
One solution we're looking at is an additional fuel tank. Another 36 gallons gets us 360 miles farther along our way. One thing you don't to do with a diesel is run it out of fuel. The restart process isn't impossible, but it's a pain in the ass.
When we finally reach the road, we'll be another 2,000 pounds heavier, but we're encouraged by our first foray into diesel RVing.