The same thing happened to me, it just keeps getting taller and wider. I have to prune it multiple times a year. It is beautiful and smells amazing, so I really hate to try to move it. Let me know how it weathers the move, if you do end up moving it. It might give me courage!

I have to keep pruning mine every year right after they bloom.

The Bunnies prune mine too low every winter....

Try Pruning them to the ground(refresh pruning)when dormant, leave some of the smaller brances if you like and just prune out the huge branches.
Yes they get 6 feet tal, but if you prune them back severely you will have a reasonable size plant for a while again.

I have a couple of these lilacs in my yard and I cannot seem to get them to get much taller than about 4-5 feet. I have fairly loose, sandy soils and somewhere between partial and full sun. I would actually like to see mine get to 6' tall!