I installed the maps on my 3790T a few months ago. I've not encountered any of the problems you describe. Did you install the maps on a memory card? It may be your microSD or the version of maps you installed.
I do notice that when using my microSD, every two weeks or so, the maps "slow down" or freeze but Nuvi just restarts/reboots itself. But I attribute that to me leaving Nuvi in standby instead of turning it completely off.
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