'Catawba' is a popular choice. 'Zuni' is another purple selection but I have never seen it planted anywhere.

I have 'Yuma' which is performing well, but it's more lavender than purple.

since you are talking about a dwarf cultivar, i'll recommend 'chickasaw' which is one of the first ones released a few years ago. supposed to grow to about 20" tall. the color is pale lavender to me though sources describe it as pinkish lavender. i think it complements pinks, whites and other soft colors well.
these dwarfs are nice additions to beds and borders for their long bloom periods.
no fall color for me on this one.

'Zuni' grows 9 feet tall by 8 feet and is display in some web photos to appear more pink than purple,

But lots of those same web sites list it as a lavender bloomer. Only one web site I saw listed it as a purple bloomer, while also showing a photo of it displaying more of a deep bluish pink shade of bloom color.

They report the leaves turn orange red in the fall.

Those sites also suggest it is best trained in the form of a very nice looking small tree.
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alicia, is nine feet, taller than what you are looking for? If not, the 'Catawaba' cultivar can grow up to 6 feet taller than that. Photos on the web of it growing can be seen where it appears really nice and displays a nice shade of purple blooms, they grow with more of a vase shape, especially if while fairly young, the trunk legs are kept clean, once they mature their canopies top out like a rounded dome. Some webs sites list them as growing 15x14 feet and others only list it as a 10 - 12 feet tall grower. Other people report being discouraged, that for them, the tree bloomed violet instead of purple like they first expected.
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'Velma's Royal Delight' is reported to grow 6-8 feet tall, produce Deep purple flowers; and if the leg tunks are not cleaned, it forms a wide spreading shrub which is good used to block the view of things like dumpters or the back side of a ground- installed satellite dish.
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'Dwarf Royalty' is reported to grow 4-8 feet tall, produce royal purple blooms, display a tan exfoliating bark, have good mildew resitance, but no special interest fall leaf color change.
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'New Orleans' is a miniature, weeping, rich purple bloomer. it grows in shrub form to only 2-3 feet tall.

The 'Petite Orchid' cultivar grows in a dwarf upright form, 4-6 feet tall.

These last two listed cultivars only have a fair mildew resitance and no special fall leaf color change.

Velma's Royal Delight, Dwarf Royalty and New Orleans sound like they are the closest to what I'm looking for, more of a purple purple than lavender purple. Thanks everybody for your input.