Doesn’t sound right at all. We’ve “lived with” the Nuvi 350 for about a year with no complaints. The performance has been outstanding. FWIW, the unit needs to “see” 3 satellites to find its location — 4 or more (of the 27 in the constellation) is better.
Where do you have it located — the front windshield is where ours is, but it will work fine just held in your hand or sitting in your lap. I’ve used the Garmin handheld GPS units for years — inside a boat. Never needed an external antenna, but, again, its mounted near a windshield, so it can “see” at least a third of the sky at all times.
I have placed it on all parts of the windshield within sight excluding those that would cause me to not see the road.
Three satellites are needed to establish a position on the surface while a minimum of four are required to calculate altitude.