Good morning,

Could anyone please recommend a reputable specialist for PowerShift transmission repairs? I have been advised over the phone by one transmission technician that the issue may relate to one of several components, potentially the valve body, mechatronic unit, clutch, or gearbox. However, I have noted a number of unfavourable reviews regarding that particular provider, and I am therefore seeking alternative recommendations.

The current symptom is that the vehicle is only shifting up a single gear and is also juddering during operation.

Thanks

Whilst it may well be an internal problem (advice over the phone doesn't actually sound like any real diagnosis has been applied - are there any Forscan codes confirming?), I'll make my usual boring suggestions...

What is the oil and filter change history?
If it hasn't been changed in a couple of years (or less), change it, I use:
https://www.ebay.co.uk/itm/112436788478
or even cheaper:
https://www.ebay.co.uk/itm/286550759056
Obviously, you know the drill in that the side plug is NOT just a level plug and the process to change needs to be done correctly:
https://www.youtube.com/watch?v=CERqRSK2SWM
Tear the filter apart and inspect.
Test all electrical connections from TCM to PCM.
Check earth straps.
Now some of these may be totally useless but they are all MUCH cheaper than a transmission rebuild.
You will know that you have done everything possible external which is good if it has to be refurbished.

Sorry to not answer your question which I'd suggest can only be done by a Google Maps search for transmission specialists in your area, looking at their reviews and especially warranty (2 years?) and visiting to see what their workshop looks like to gain some confidence.
In our area there's:
https://austrin-engineering.co.uk/services/
There appear to be "cheap" transmissions on e-bay but I'd prefer mine to be rebuilt if that was the route however if the car doesn't have much life then a cheaper one may be more sensible?
The risk is that you want one company to be responsible for the entire job so any problems are down to them to fix?
Do let us know how you get on!

Edit: This lot seem to get good reviews on Google Maps (that's all I know) but there are other suppliers that may be nearer:
https://www.ebay.co.uk/itm/187329476809