At the beginning of every journey, my van doesn't want to shift into 4th for the first 40 - 60 minutes of the journey. Once it has done so, the shift is smooth as butter and for the rest of the journey it will shift in and out without any trouble. If I kill the engine, even for a few minutes, the problem reappears.

I'm hoping it's just a sensor somewhere, the tranny fluid looks to be at a good level (maybe even a bit on the high side) and not discoloured. It's a pretty irritating problem though, travelling 45 minutes to town in 3rd for it to shift into 4th as I arrive isn't good for my wallet, and can't be good for the car as a whole.