You have done the best things you could for this plant. It is stressed enough with the previous poor location and the transplanting. I would not give it a hard prune until it is healthy. If it is too tall, you could cut the top back, but I would not remove more than 30% of the green leaves. Less is better in this case.

Next spring I would give it a shot of Holly-tone before it blooms.

I have 6 of those little beauties in my garden.
Next year, right after the bloom AND if it is healthy just SHEAR it.
It will look ugly (banch of bare brown twigs and nothing else) right away, but in a month and a half or two you'll have a perfectly rounded mounded shrub. I do that every two years and that keeps them full at 3' wide and not more than 2' tall.

Great tips. Hope you don't mind me asking a question, diy... ego - when you shear purple gem (which is what I think I'll do next year), does it still have lots of time to form flower buds for the following year?

If you shear it RIGHT after the bloom or even better when some flowers are still present, but majority are gone, you'll have a nice bloom next season.
With such a plant as PG you practically can't do a deadheading, so by shearing it you'll perform two tasks in one: removing spent seadheads and promoting branching.

Thanks for the great advice. I'm glad I haven't made the situation any worse for this plant. Will just watch it through next spring and hope for the best.

Thank you very much, ego... I have noticed that you can't really deadhead the purple gem easily after trying to remove a couple of the spent flowers, so I gave up. I will shear it at the time you recommended, next year. Thanks again.