Where are you located? What is in the pot that the tree is planted in (soil media)? How is it watered? Is there a reason why the tree cannot be planted in the ground?

There are all kinds of reasons why your tree is not performing the way you hope and it is very likely that trying to grow it in a container is accounting for a lot of them. Unless one is accustomed to growing trees in containers, it can be very challenging. We need more information to help you.

No reason it can't be planted in the ground. We just didn't plant it that way as the centre we bought if from.said it was last in the pot for a few more years. Soil in the pot is same as that we bought it in.

In the summer we water it every 2-3 days (or more regularly if really hot).

Happy to replant it if that's what's best.

Is my tree beyond saving?

No, it is not beyond saving.

Unless one is working with a very durable potting mix (bark based) and a generously sized container, root pruning and repotting with fresh media should be done every couple of years, if not more often. And a tree grown in a container will need routine fertilizing as well.

Planted in the ground in decent soil and with suitable exposure, you will not need to worry about any of that. And once established, watering frequency will be greatly reduced as well. I would plant it in the ground.

You can prune out any dead wood at any time and it is actually recommended to do so when you see it, as it can harbor insects and allow diseases to make inroads. Fully dead wood will take on a very pale, almost silvery-gray coloration. And some, even on very healthy JM's, is to be expected. An excessive amount, specially during the growing season, is an indication that the tree is not getting the care it needs, whether that be adequate water or root and potting soil attention.

Once planted in the ground it will grow much better. However, it may outgrow that location, depending on the cultivar.