If its 10 degrees cooler at that altitude,my guess would be the temperature.It doesnt take much.
Need more info about your Prados starting habits and which engine.
Does it run rough and smooth out after a while or does it crank over and take a while to fire ?
Don't know anything about a Prado but you do loose 3% of power for every 1,000 increase in elevation. Low compression units have a harder time starting at higher elevation do to the reduction in atmospheric pressure.
You should not notice any change with only a 1,600 increase in elevation from sea level.
i would gamble it is the temp change. elevation will not affect the starting, it will affect the performance, fuel economy but not starting since starting is controlled by glow timing, battery strength (speed of rotation), compression ratio and fuel supply...
disconnect the glow plug water temp sensor on the side of the engine to have full glow time duration and see if that helps.