Semi auto box, appears to slip when going to a higher gear

The only way you will find out the answer is to get it checked for fault codes with suitable diagnostic equipment .

Wonder if the level is okay in the box as may explain why driving ok when temperatures are up and fluid is circulated ,worth a check

just spoke to a mechanic, first thing he asked was "has the battery been flat at any time recently?" the answer was yes, I changed the fuel and air filters and had the thing turning over but flattened the battery and had to re- charge it!
Seems the confuser may have forgotten how to change gear and needs to be retaught, rather like myself!
So fingers crossed and and a bit of folding stuff I may have the answer, will keep site posted with results.

Quite common on various make that they have to go through a relearn sequence which varies from car to car . Not sure but that car may have a sealed gearbox which means you have to drain and refill with correct amount rather than older conventional boxes which were simple to top up if needed . Thanks for updating the forum , hope it cures the problem .