Answer: It sounds like the shrub might be a candidate for some renewal pruning to encourage vigorous new growth. Lilacs bloom on "old wood" meaning the previous year's growth, so do any pruning in the spring immediately after they bloom (or in early spring before they bloom if you don't mind sacrificing the current year's flowers.) There are two methods of doing this. The drastic method is simply to cut the whole thing off at the base, as close to the ground as you can. This will result in many suckers growing up from the roots which will then be thinned every spring.
Lilacs will grow in the alkaline soil in your region, but will not be a dependable performer because lilacs need a pronounced winter chill to produce flowers. There are a few hybrids developed by Descanso Gardens that will bloom without a winter chill. If yours is 'Lavender Lady', 'Blue Skies' or 'Forrest K. Smith', it will bloom for you. If not, you might want to think about getting one of them instead of moving your lilac.
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