I honestly haven't researched the results of an H42's or H55's mileage vs the A440 but I am surprised it could be as dramatic as a 33% loss in fuel efficiency, especially with the A440 robbing more power than the manual gearbox.
At least I can consider you are driving from Texas vs driving from, say, Wyoming (kind of an opposite style trip). Do you drive hammer down or at 55? The details matter the most if you are analyzing a situation. If you drive hard, you want your average or 95th percentile speed to coincide with the engine's peak torque.
If it were me, I would take my time on the trip knowing that driving 55mph is going to give the best fuel economy and be otherwise more relaxing. It is easy and comfortable to do in an FJ62 with 33s and an H42. The 3FE likes to rev, the 2F does not as much (though it can take it pretty well). I would also not have a roof rack on if I only cared about economy. But I approach trips differently I guess. I commit to a trip and do not worry about gas prices so much. If I am committed I know I will spend some unknown amount on fuel because I don't know what fuel costs everywhere. I am not designing my truck just to make the cost of fuel cheaper; the Land Cruiser is my vehicle because it does what it does so well (carrying capacity, slow speed control, uncanny reliability, ease of repair in the field, simple/effective design), not because it is efficient at going long distance.
I also know that I want to *enjoy* the trip and not have to race to a destination so I am not going to haul *** along an Interstate. You would be surprised at how much quieter the cabin is driving 55 vs 70 or 75.. there are a lot of things that can make a trip more relaxing. Ok maybe I'm showing my age, but finally I have been able to do trips lately where I am not exhausted when I return home; I am refreshed (and that is one of my goals for trips). Again, I drive to the engine, and with respect to that I often drive what the engine likes to drive at. I look at EGTs, I look at coolant temps, I have a certain visceral feedback/feel of how it is doing and I drive to the maximum efficiency of that situation when I am able to. Much of that has been becoming more patient, and I am learning. :ylsmoke:
When I did the HZ-t/H55 swap, my goal was ultimate range because I am more often than not doing very long distances (200-500 miles) solely on dirt/rock tracks (5-15mph) and I got tired of worrying about where I had to plan to break out for fuel. I also wanted to get over passes without drama. I have done this in mini/hilux's, the '64 FJ40, the BJ42s, the '79 FJ40 and now the FJ62. I knew the new HZ/H55 was not the ultimate but it was 95% there for me. With the turbo I know if I have to I can drive 75-80 over Interstate and still get 19mpg. But I can drive 55 and get 23 with a quieter cabin, softer music, easier conversation, a chance to see the countryside, etc.. If I could have afforded the $5000 in upgrades to get the A440 into shape that would have handled the HZ-t's torque, I would have done that because I think the A440/2 is one of if not the best Toyota transmission. It was just more advanced than the motor unfortunately. Keep in mind that my freak of a truck at 60-70mph cruising long distances would get 16-19mpg with the factory drivetrain on 31s. 33s, armor and gear load dropped it to 15-17. I didn't have the 29-30"ish tires on long but I am sure it would be in the 20s. It was a well maintained and tuned truck (I got it at 175k).
Not yelling, just trying to get closer to the whole story rather than focus on one aspect of an analysis. :elkgrin:
I'm going to shutup now.