It definitely sounds like a bad unit. I only have that trouble with my eTrex when I'm in very heavy timber and mtns in Colorado.

One interesting thing happened about 6 years ago. I actually got an incorrect reading just north of Ouray, Colorado when standing next to a large cliff. I triple checked my readings and wrote them down, and as I moved away from the cliff, about a mile or two, it corrected itself. Talk about not instilling confidence....