Locking the thread on the 7 inch display Nuvi 57 map connection issues got my attention. Since the sleep issue may be unique to the Nuvi 57, which may draw nearly twice the power of the smaller Nuvis, it could have been a computer USB port power supply issue. Getting the maps correctly installed and linked on the computer may have hidden the Nuvi device power draw issues. Perhaps the computer Device Manager USB power setting needs some tweaks too.
That's all just speculation, as I only connected the maps on my 5 inch Nuvi 56 once before finding I could download the same version of the maps to Basecamp.
Quick fix might be to turn down the brightness (power draw) on the 7 inch Nuvis.