You're probably right in that the reason it doesn't fruit is due to the shade, but it sounds like a rather large tree to try to transplant. If it blossoms, but gets no fruit, then the issue is more likely lack of pollination, late frosts, or curculios. It might not be hardy enough for zone 5. Unless the issue is shade, transplanting it wouldn't help, anyway. Maybe you could plant another compatible and hardy variety in a sunnier spot and then graft a couple branches from this one onto the new one. Mt. Royal is a hardy European plum. Northwoodswis

If you can graft or know someone who can, you could get wood from another plum that is known to pollinate the plum you have. I'd guess pollination is your problem.

Thanks for the info. I was under the impression from the catalog that it didn't need a pollinator but we could still try that. The tree is roughly 7 or so years old and is barely over 5ft tall and very spindly. It's supposed to be a dwarf variety.

If transplanting is still an option how would be go about doing that safely without damaging the poor tree?

Stanley is very unlikely to have a problem with the weather in zone 5.

I've seen Stanley called self-fruitful, and I don't think that is true.

You need another plum, and it has to be another European plum, not a Japanese plum.

If you are wanting to move her, then wait until spring and move the tree when she's fully asleep, but late enough that the soil should start to warm up a bit after she's moved, so she can start sending roots out.

If you get no blooms, the flower buds are freezing. If you get bitty fruit that falls off, you have a pollination issue.

One last possibility is that you purchased a mislabeled tree, like I did. My "Stanley" finally produced fruit this year and my "Stanley" isn't a Stanley.

Since we are talking about Pollination I have a pear tree I don't know what is it. It was sold to me as Bartlet I don't think it is. It produces lots of pears but small ones and aside from the Bugs the fruit is sower and has no sugar.Could this due to lack of pollination.
Why Nurseries cheat and never tell you what you are getting. They know that you will discover in few years and by that time either they are out of business or you forgot their name.

Stanley is self-fruitful. Most European plums are.

Thanks everyone for all the help! I will pass the info on and we will likely both move the tree and get a pollinator for her just in case. We've a lovely sunny spot behind the towering spruce trees and on the south side of our house where hopefully our little plum will be happier. Again, thanks muchly for the help!

Stanley is self fertile, and will bear without a pollinator.....but, it will produce more fruit if it has another European plum pollinator.

I suspect the reason your fruit fell off before maturity was PC (plum curlico). They decimate almost every Stanley tree in Michigan.

As for the idea of moving a mature fruit tree, or picking one up at Meijer or English Gardens for about 20 bucks.....I would do the latter. They also offered Green Gage trees this year.