Jerry
Welcome to the world of SWB Prados.
There is nothing wrong with the electric hubs, in fact they are actually stronger than, I think,
any of the aftermarket ones. Mine have lasted 157 k so far including 80k driven by me of which 25% is off-road.
The problem with them is the carbon brushes that drive the wee motors. When people reassemble them after having been beyond them into the hubs, they often dislodge the correct position of them. They should be reassembled with a small piece of wire holding the brushes up as the units are installed, then the wires can be pulled out allowing the brushes to settle in their correct position.
I too would suggest getting OldBlues mod, something I have yet to do.
In terms of the inevitable head demise, all the 4cyl turbo diesel Toyo engines do this. I think the design brief did not include foot-up-it driving with trailers behind. I have only tonight just driven for an hour down from the hills sitting between 100 to 140 k's with my trailer behind

The great thing about the Prado is you don't really notice any handling difference with the trailer on.
I digress, back to heads. Two months ago when my 1kz-te head went, we had a good look at the cooling system and eventually only replaced the top plastic radiator tank as a precaution, (they crack with age.) They cleaned out the core but it was actually fine to start with. Yet when Diesel Pumps stripped out the injectors the sealing washers showed signs of having got way too hot.
My point is these motors don't have to get the cooling system hot to get the aluminium head to fatigue crack. The internal combustion temperatures reached under sustained high load but slow revs (I.E. Lugging) or sustained load at high revs (I.E. my driving home late tonight) cause a temperature build up that the water galleries within the head are not capable of removing quickly enough to maintain the correct internal temps.
The advise I have been given is
1) Remove the Exhaust Gas Recirculation system (EGR) - who wants to shit in their own nest anyway

Adding hot exhaust gases to the inlet system can only add heat to the engine.
2) Fit a Pyrometer (Exhaust gas temperature gauge), best place is in the manifold prior to the turbo BUT you need to do this with the Ex Manifold off the engine/turbo - swarf is nasty on turbine vanes. Other place is just after the turbo but temp readings are about 100 degrees lower.
3) Fit a low back pressure exhaust system, 2.5" or bigger in your case, 3" in my case. You need to do this all the way from the turbo. My race tuning shop mates tell me there are big gains to be had on the 2lt turbo outlet casting because the factory outlet is incredably restrictive. This means dismantling the turbo, so not always everyones cup of tea. The exhaust system also needs to include a low back pressure muffler. The plus of all this work is that the turbo spools up much quicker giving a lot more responce and a flatter torque curve which is great off-road.
4) If like me ,your right foot is made of lead, fit an intercooler. It seems from other threads on here that Nissan Silvia ones do the job, as do Subbie ones.
In terms of Toyota gauges, whilst my engine was apart I took the trouble to get my oil pressure and water temp gauges along with the actual sender units checked by Parrots in Christchurch. I and later Mike have bought our Pyros from Parrots as well. The outcome of this was that the gauges read fine BUT the range of movement between 75 and 110 degrees is minimal.
When I find that roundtuit I shall post a thread along with some photos on this subject.
ENJOY YOUR PRADO
Cheers John