S Type 51 plate 4.0 Transmission repair

I'm looking for a recommendation or club member into such things to repair the auto box on my car. She's done less than 60k miles but doesn't like going into top gear. My research has come up with the box type as the 5R55N made by Ford. I believe the issue is the solenoid pack that can either be serviced or replaced. I would just like it to work, so if you lovely Jag owners out there can recommend someone you have dealt with and trust to get the job done, it would be greatly appreciated!

I am based in the Southwest and would appreciate someone qualified in the vicinity.

Thanks in advance, Lyndon