So, as of 2230 pacific time (we're running the trip on Pacific, since we are starting and ending on it) last night, we've made 862 miles, in 15.5 driving hours plus 2.5 hours of meal and gas stops.
Our driving average is 55mph; and excluding overnights, we're making a real average of about 49mph.
It's not so much that we're "taking our time", it's really a combination of three things:
1. the trailer prefers to be driven between 63 and 72mph. Below that and we're a gear low to keep in powerband (and yes, you need to keep in powerband when you're towing a heavy trailer) and the fuel economy goes to hell. Above that, and the trailer sways more than is prudent, and the fuel economy goes to hell.
2. We've transited several major urban areas, across Arizona, Nevada, and Utah; in ALL of which was extensive construction. Also, we were on a 55mph piece of road the entire time we were in CA (us 95), and it actually IS a 55mph road, with lots of tight curves, whoopdedos etc... (it would be nice on a motorcycle, at a leisurely pace).
3. We spent a lot of time on long and steep uphill grades. We've basically been climbing the entire time since we left Phoenix; climbing from Phoenixes 1200 or so feet, to Ogens 4300 or so feet, summiting around 6500 somewhere in south central Utah.
Once we hit the plateau in between the big passes in central Utah, we were able to maintain an almost 70mph average; and our fuel economy went up to 12.8mpg, our best at 70mph for the trip. Our best overall for the trip was 14.8, but that was on a flat, smooth stretch of highway with no stop and go, but traffic restricted to 60mph for about 100miles.
Our worst mileage for the trip so far is 8.4mpg, on several of the long, steep grades; where we were lucky if we could maintain 3rd gear.
Our normal unladen fuel economy is 16-18mpg around town, and through the mountains, and 21-24mpg highway (depending on how much we put the boot to it). So yeah, it's a big drop, but it's actually a lot better than most trucks would be (a gas truck hauling this same load would likely be 5-7mpg), and it's about what we figured on.
We're going to be on the road again shortly... After checking the load, the lugs on the trailer and the truck, tire pressures and topping fuel and fluids (which we do at every fuel stop. You don't mess around when towing heavy loads).
We've got 694 miles to go, no more major urban area (Pocatello, Idaho Falls, Butte, Missoula, and Couer D'Alene, none of which count as major) to transit, and only a couple major grades to deal with (coming out of dubois up to Butte, then into and out of Missoula, and through lookout pass over to Coeur D'Alene) we should be able to up the average quite a lot. I think we can maintain 70mph most of the way, and average 60mph including stops for today.
We plan on making it to the house late tonight, with 12 driving hours, and 14-15 total hours (which is about what we did yesterday) under the tires.
Should be pretty.