I believe your transmission is probably working just fine. You are probably testing the 3rd start feature on pavement where there is neither slipping nor very poor traction.
Try it on very slippery conditions where there is very (extreme) poor traction, and you will find that it will start in low, as per normal, but immediately upshift to give you a 3rd gear start capability, with minimal wheelspin.
If you use the shift knob to select 3rd gear under these same slippery conditions, you will find that the transmission will not upshift right away but will continue to spin the wheels, through all the gears up until 3rd.
Post again if I did not explain to your satisfaction. I'm retired, I have the time.
On another matter;
By the way, I may have not understood correctly your original post. My apologies, if I am wrong. I understood that you drove your vehicle on dry pavement with 4X4 engaged. This is a no-no!
On the Alterra, unlike full-time 4X4 systems, there is no front to rear differential action. This means that on pavement, the front axle has a tendency to "lock-up" with the rear axle since there is no slipping on the pavement. This is detrimental to tires, and could lead to difficulty in the 4X4 engagement and disengagement process. Since this process (engagement/disengagement) is electric on the Alterra, rather than via linkage, you would not be aware of the strain placed on the four wheel drive components.
Part-time 4X4 operation, such as is on the Alterra, especially since it has a limited slip rear differential, is just plain excellent for off-road and/or back roads applications.......but not designed for pavement driving, unless there is snow and/or ice (Or mud/flood) conditions.
If you were to always drive in a 100% straight line, you would not have any concern about "lock-up". But when you turn the vehicle, even slightly, or a wheel goes over a depression or bump in the road, the right wheel does not turn as much (or more) than the left wheel. Your differential takes care of this problem for you.
On a four wheel drive vehicle, the problem is even worse. a front wheel could travel more (or less) rotations than a rear wheel. Thus there is a need for a front to rear differential action such as found on full time four wheel drive systems.
But, don't run out to buy a full time system to replace your part-time system. If a full time system does not employ a limited slip differential, you could find yourself stuck with only one wheel spinning, and that would be the wheel with the least traction. So you would go nowhere.
For me, I very much prefer part-time four by four with limited slip on the rear axle, and freewheeling hubs on the front. It does not get much better than this except with a Kubota four wheel drive field tractor.
Ciao!
Uncle Nick.



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