Actively considering cancelling reservation.

[KevinRS]

That tow test they did in Arizona wasn't for a commercial, it was part of the SAE standard for tow ratings. The trailer was filled with weighed sandbags to exactly meet the rating they were going for, and there are several tests they have to do. An acceleration test, the drive up that specific grade while the ambient temp is over 104F with the AC on max, and others. The standard has something like 27 pages.

 

[AZFox]

That tow test they did in Arizona wasn't for a commercial, it was part of the SAE standard for tow ratings. The trailer was filled with weighed sandbags to exactly meet the rating they were going for, and there are several tests they have to do. An acceleration test, the drive up that specific grade while the ambient temp is over 104F with the AC on max, and others. The standard has something like 27 pages.

At 45 MPH and 104F degrees it wasn't very strenuous compared to what will happen in the real world.

FWiW, Phoenix, AZ has a lot of days with temperatures at or above 110°F every year.

Maybe the tow rating is limited by the powertrain,'s capability.

 

[KevinRS]

That part of the test is a 7% grade, average 5% and a 11.4 mile drive gaining 3020 feet. How does that compare to other real world hot weather grades? In phoenix sure it's hotter, but it's also flat.
I looked up the grade in my area which is considered challenging for trucks, and it's a sustained 6% for 5 miles, but that's mostly a problem for downhill travel with truck brakes failing.

SAE J2807 Tests

Test	SRW	DRW
Davis Dam	>=40 mph	>= 35 mph
Go 5 meters from stop on 12% grade, 5 times in a row	<= 5 minutes	<= 5 minutes
Hold full rig with just parking brake	12% grade	12% grade
0 - 30 mph(level ground)	<-= 12 sec	<= 14 sec
0 - 60 mph(level ground)	<= 30 sec	<= 35 sec
40 -60 mph (level ground): passing test	<= 18 sec	<= 21 sec
20 mph to stop with trailer brakes active, staying in 11.5 feet lane, trailer lighter than tow vehicle	<= 35 ft	<= 35 ft
20 mph to stop with trailer brakes active, staying in 11.5 feet lane, trailer heavier than tow vehicle	<= 45 ft	<= 45 ft
20 mph to stop without trailer brakes, staying in 11.5 feet lane, trailer lighter than tow vehicle	<= 80 ft	<= 80 ft
understeer test: increases from 0.1 g to 0.3 g n 300 ft circle	pass	pass
sway test, 62 mph	>= 1.0 damping ratio	>=1.0 damping ratio

I think it's not just the powertrain that they are setting the 1000 lb limit by. They knew from the start about things like the range issues towing with the Lightning, and that they would be even worse with a relatively lightweight and low range Slate with any larger load, especially with any significant cross section to the wind, so they set 1k as the target and engineered for it. So the powertrain, frame, everything may all be limits if you were to try to increase the towing capability safely.

The other possibility is that if the truck is mechanically capable of towing more, the range may be so reduced that it becomes useless.