Ok as the title says, the wagon has developed a lovely new habit. Normal driving there is no problem but under moderate acceleration as she's going through the gears, 1st to 2nd is fine, 2nd to 3rd on occasion shudders, and 3rd to 4th at about 80kph and about 2000rpm she shudders and seems to not engage 4th properly, but after about 4 or 5 seconds of this she'll drop into gear just fine.
Under firm acceleration and when she's not in 'econ' mode she behaves just fine. I'm not 100% sure it's a trans issue, I'm also thinking it could be blocked up fuel filter / injectors maybe? But any other thoughts or opinions you guys might have could help.
Thanks.

Service the auto and change the diff oil and see how you go.

I should have been a bit more specific in my original post, but now she's done it a few more times I can give a better description of the problem.
The issue is as described before but it seems like it's the engine itself missing/cutting out/loosing power under moderate load, but only at the change points from 2nd to 3rd and 3rd to 4th and only ever around the 2000rpm mark. When I have the trans in Pwr mode, or accelerate hard and force it to hold the gears she's fine. Hence my confusion.
The trans was replaced 3mths ago, so it shouldn't need servicing (I hope )